Laser induced graphene materials and their use in electronic devices

ABSTRACT

In some embodiments, the present disclosure pertains to methods of producing a graphene material by exposing a polymer to a laser source. In some embodiments, the exposing results in formation of a graphene from the polymer. In some embodiments, the methods of the present disclosure also include a step of separating the formed graphene from the polymer to form an isolated graphene. In some embodiments, the methods of the present disclosure also include a step of incorporating the graphene material or the isolated graphene into an electronic device, such as an energy storage device. In some embodiments, the graphene is utilized as at least one of an electrode, current collector or additive in the electronic device. Additional embodiments of the present disclosure pertain to the graphene materials, isolated graphenes, and electronic devices that are formed by the methods of the present disclosure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/940,772, filed on Feb. 17, 2014; and U.S. Provisional PatentApplication No. 62/005,350, filed on May 30, 2014. The entirety of eachof the aforementioned applications is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant No.FA9550-14-1-0111, awarded by the U.S. Department of Defense; Grant No.FA9550-09-1-0581, awarded by the U.S. Department of Defense; Grant No.FA9550-12-1-0035, awarded by the U.S. Department of Defense; and GrantNo. N00014-09-1-1066, awarded by the U.S. Department of Defense. Thegovernment has certain rights in the invention.

BACKGROUND

Current methods of making graphene-based electronic materials havenumerous limitations in terms of manufacturing efficiency and electricalproperties. As such, a need exists for more effective methods of makinggraphene-based electronic materials.

SUMMARY

In some embodiments, the present disclosure pertains to methods ofproducing a graphene material. In some embodiments, the methods includeexposing a polymer to a laser source. In some embodiments, the exposingresults in formation of a graphene that is derived from the polymer.

In some embodiments, the exposure of the polymer to a laser source alsoincludes a step of tuning one or more parameters of the laser source. Insome embodiments, the one or more parameters include, withoutlimitation, laser wavelength, laser power, laser energy density, laserpulse width, gas environment, gas pressure, gas flow rate, andcombinations thereof.

In some embodiments, the laser source includes, without limitation, asolid state laser source, a gas phase laser source, an infrared lasersource, a CO₂ laser source, a UV laser source, a visible laser source, afiber laser source, a near-field scanning optical microscopy lasersource, and combinations thereof. In some embodiments, the laser sourceis a CO₂ laser source.

In some embodiments, the polymer is in the form of at least one ofsheets, films, pellets, powders, coupons, blocks, monolithic blocks,composites, fabricated parts, electronic circuit substrates, andcombinations thereof. In some embodiments, the polymer includes, withoutlimitation, homopolymers, block co-polymers, carbonized polymers,aromatic polymers, vinyl polymers, cyclic polymers, polyimide (PI),polyetherimide (PEI), polyether ether ketone (PEEK), and combinationsthereof. In some embodiments, the polymer includes a doped polymer, suchas a boron doped polymer.

In some embodiments, the exposing of a polymer to a laser sourceincludes exposing a surface of a polymer to a laser source. In someembodiments, the exposing results in formation of the graphene on thesurface of the polymer. In some embodiments, the exposing includespatterning the surface of the polymer with the graphene. In someembodiments, the graphene becomes embedded with the polymer. In someembodiments, a first surface and a second surface of a polymer areexposed to a laser source to form graphenes on both surfaces of thepolymer.

In some embodiments, the exposing of a polymer to a laser source resultsin conversion of the entire polymer to graphene. In some embodiments,the formed graphene material consists essentially of the graphenederived from the polymer. In some embodiments, the methods of thepresent disclosure also include a step of separating the formed graphenefrom the polymer to form an isolated graphene.

In some embodiments, the formed graphene includes, without limitation,single-layered graphene, multi-layered graphene, double-layeredgraphene, triple-layered graphene, doped graphene, porous graphene,unfunctionalized graphene, pristine graphene, functionalized graphene,turbostratic graphene, graphene coated with metal nanoparticles, metalparticles coated with graphene, graphene metal carbides, graphene metaloxides, graphene metal chalcogenides, oxidized graphene, graphite, andcombinations thereof. In some embodiments, the formed graphene includesporous graphene. In some embodiments, the formed graphene includes dopedgraphene, such as boron-doped graphene.

In some embodiments, the methods of the present disclosure also includea step of incorporating the graphene material or the isolated grapheneinto an electronic device. In some embodiments, the electronic device isan energy storage device or an energy generation device, such as a supercapacitor or a micro supercapacitor. In some embodiments, the grapheneis utilized as an electrode in the electronic device. In someembodiments, the graphene is utilized as a current collector in theelectronic device. In some embodiments, the graphene is utilized as anadditive in the electronic device.

Additional embodiments of the present disclosure pertain to the graphenematerials and the isolated graphenes that are formed by the methods ofthe present disclosure. In some embodiments, the graphene materialincludes a polymer and a graphene derived from the polymer. In someembodiments, the graphene is on a surface of the polymer. In someembodiments, the isolated graphene is derived from a polymer andseparated from the polymer.

Further embodiments of the present disclosure pertain to electronicdevices that are formed by the methods of the present disclosure. Insome embodiments, the electronic device has a capacitance ranging fromabout 2 mF/cm² to about 1,000 mF/cm². In some embodiments, thecapacitance of the electronic device retains at least 90% of itsoriginal value after more than 10,000 cycles. In some embodiments, theelectronic device has power densities ranging from about 5 mW/cm² toabout 200 mW/cm².

DESCRIPTION OF THE FIGURES

FIG. 1 provides schemes and illustrations related to graphene materialsand isolated graphenes. FIG. 1A provides a scheme of methods of makinggraphene materials and isolated graphenes, and incorporating theproducts into electronic devices. FIG. 1B provides an illustration of aformed graphene material 20. FIG. 1C provides an illustration of aformed electronic device 30. FIG. 1D provides an illustration of aformed electronic device 40.

FIG. 2 provides data and images relating to laser-induced graphene (LIG)formed from commercial polyimide (PI) films using a CO₂ laser at a powerof 3.6 W to write patterns. FIG. 2A is a schematic of the synthesisprocess of LIG from PI. FIG. 2B is a scanning electron microscopy (SEM)image of LIG patterned into an owl shape. The scale bar is 1 μm. Thebright contrast corresponds to LIG surrounded by the darker-coloredinsulating PI substrates. FIG. 2C is an SEM image of the LIG filmcircled in FIG. 2B. The scale bar is 10 μm. The inset is thecorresponding higher magnification SEM image with a scale bar of 1 μm.FIG. 2D provides a cross-sectional SEM image of the LIG film on the PIsubstrate. The scale bar is 20 μm. The inset is the SEM image showingthe porous morphology of LIG with a scale bar of 1 μm. FIG. 2E is arepresentative Raman spectrum of a LIG film and the starting PI film.FIG. 2F is an X-ray diffraction (XRD) of powdered LIG scraped from thePI film.

FIG. 3 provides images of materials and equipment for production of LIGfrom PI by laser scribing. FIG. 3A provides photographs of commercialKapton PI sheets (left) with a 30 cm ruler, and the laser cutting system(right). FIGS. 3B-C provide photographs of an owl and a letter Rpatterned on PI substrates. The scale bars are 5 mm. In FIGS. 3B-C,black contrast is LIG after exposure to the laser, while the lighterbackground corresponds to PI. The laser power used to scribe the imageswas 3.6 W.

FIG. 4 provides Raman spectra of control samples. PI sheets werecarbonized in a furnace under Ar flow of 300 sccm for 3 h with thefollowing annealing temperatures: 800° C., 1000° C. and 1500° C. Ramanspectra show that these carbonized materials were glassy and amorphouscarbon.

FIG. 5 provides x-ray photoelectron spectroscopy (XPS) characterizationof LIG-3.6 W films (i.e., LIGs formed by exposing PI sheets to laserspowered at 3.6 W). FIG. 5A provides XPS surveys of LIG and PI.Comparison curves show that the oxygen and nitrogen peaks weresignificantly suppressed after PI was converted to LIG. FIG. 5B provideshigh resolution C1s XPS spectrum of the LIG film and PI, showing thedominant C—C peak. The C—N, C—O and C═O peaks from PI were greatlyreduced in the C1s XPS spectrum of LIG, which indicates that LIG wasprimarily sp²-carbons. FIG. 5C provides high resolution O1s XPS spectrumof a LIG-3.6 W film and PI. After laser conversion, the C—O (533.2 eV)peak becomes more dominant than C═O (531.8 eV). FIG. 5D provides highresolution N1s XPS spectrum of a LIG-3.6 W film and PI. The intensity ofthe N1s peak was greatly reduced after laser exposure.

FIG. 6 provides Fourier transform infrared (FTIR) spectra of LIG-3.6 Wand PI films. FTIR spectra of PI show distinct peaks at 1090-1776 cm⁻¹,corresponding to the well-defined stretching and bending modes of theC—O, C—N, and C═C bonds. After the laser scribing, a broad absorptionfrom 1000 cm⁻¹ to 1700 cm⁻¹ shows that the laser scribing leads to alarge variation in the local environment.

FIG. 7 provides a transmission electron microscopy (TEM)characterization of LIG-3.6 W flakes. FIG. 7A provides a TEM image of athin LIG flake atop a carbon grid. The scale bar is 200 nm. FIG. 7Bprovides a TEM image of a thick LIG flake showing entangled tree-likeripples. The scale bar is 100 nm. Inset is the high resolution TEM(HRTEM) image of the yellow-circled region showing the mesoporousstructures. The scale bar is 5 nm. FIGS. 7C-D provide TEM images of LIGin bright and dark field view. The scale bar is 10 nm. In dark fieldview, folded graphene containing several pores between 5 to 10 nm can beseen. These pores indicated in arrows in FIG. 7D result from curvatureof the graphene layers induced by abundant pentagon-heptagon pairs.

FIG. 8 provides TEM images of LIG obtained with a laser power of 3.6 W.FIG. 8A provides an HRTEM image taken at the edge of a LIG flake showingfew-layer features and highly wrinkled structures. The scale bar is 10nm. FIG. 8B provides an HRTEM image of LIG. The scale bar is 5 nm.Average lattice space of ˜3.4 Å corresponds to the (002) planes ofgraphitic materials. FIG. 8C provides a Cs-correction scanning TEM(STEM) image taken at the edge of a LIG flake. The scale bar is 2 nm.The image shows an ultra-polycrystalline nature with grain boundaries.FIG. 8D provides a TEM image of selected area indicated as a rectanglein FIG. 8C. It shows a heptagon with two pentagons as well as a hexagon.The scale bar is 5 Å.

FIG. 9 provides a TEM characterization of LIG-3.6 W flakes usingfiltering techniques. FIG. 9A provides a bright-field TEM image of thestudied area. The scale bar is 5 nm. FIG. 9B provides a fast fouriertransform (FFT) image of the LIG sample. The area has two distinct partsthat can be seen on the indexed diffractogram FFT with the hexagonalcrystal structure of carbon with lattice parameters a=2.461 Å andc=6.708 Å. The outer circle spots are reflections of the type (10.0) or(1.-1.0), corresponding to the basal plane of graphite 00.1. The layersare, however, very disordered and produce a rotational pattern withd-spacing of 2.10 Å. The inner circle spots are type (00.2),corresponding to a d-spacing of 3.35 Å of the folded layers of graphenecontaining the cavities. FIG. 9C shows that the FFT filter uses theinner circle of type (00.2) spots and neglects the outer circle of type(10.0) spots, FIG. 9D provides corresponding filtered images from FIG.9C. The scale bar is 5 nm. The folded graphene structure was enhanced,FIG. 9E shows that the FFT filter uses the outer circle of type (10.0)spots and neglects the inner circle of type (00.2) spots, FIG. 9F showsa corresponding filtered image from FIG. 9E. The scale bar is 5 nm. Thedisordered graphene structure was enhanced.

FIG. 10 provides a BET specific surface area of LIG-3.6 W. The surfacearea of this sample was ˜342 m²·g⁻¹. Pore sizes are distributed at 2.36nm, 3.68 nm, 5.37 nm and 8.94 nm.

FIG. 11 provides thermogravimetric analysis (TGA) characterizations ofLIG-3.6 W, PI and graphene oxide (GO) in argon. Compared to GO, whichsignificantly decomposes at ˜190° C., LIG is stable at >900° C. PIstarts to decompose at 550° C.

FIG. 12 provides characterizations of LIG prepared with different laserpowers. FIG. 12A provides atomic percentages of carbon, oxygen andnitrogen as a function of laser power. These values are obtained fromhigh-resolution XPS. The threshold power is 2.4 W, at which conversionfrom PI to LIG occurs. FIG. 12B provides correlations of the sheetresistance and LIG film thicknesses with laser powers. FIG. 12C providesRaman spectra of LIG films obtained with different laser powers. FIG.12D provides statistical analysis of ratios of G and D peak intensities(upper panel), and average domain size along a-axis (L_(a)) as afunction of laser power (x axis) calculated using eq 4.

FIG. 13 provides a correlation of threshold laser power to scan rate.The threshold power shows a linear dependence on the scan rate.Conditions indicated by the shaded area lead to laser-basedgraphene-induction.

FIG. 14 provides characterizations of backsides of LIG films. FIG. 14Aprovides a scheme of the backsides of LIG films peeled from PIsubstrates. FIGS. 14B-D provide SEM images of backsides of LIG filmsobtained at laser powers of 2.4 W (FIG. 14B); 3.6 W (FIG. 14C); and 4.8W (FIG. 14D). All of the scale bars are 10 μm. The images show increasedpore size as the laser power was increased.

FIG. 15 provides characterization of LIG from different polymers. FIG.15A provides a photograph of patterns induced by lasers on differentpolymers (PI, PEI and PET) at a laser power of 3.0 W. The two polymersthat blackened were PI and PEI. FIG. 15B provides a Raman spectrum ofPEI-derived LIG obtained with a laser power of 3.0 W.

FIG. 16 provides electrochemical performances of LIG-microsupercapacitor(LIG-MSC) devices from LIG-4.8 W in 1 M H₂SO₄ with their GB-inducedproperties. FIG. 16A is a digital photograph of LIG-MSCs with 12interdigital electrodes. The scale bar is 1 mm. FIG. 16B provides an SEMimage of LIG electrodes. The scale bar is 200 μm. FIG. 16C is aschematic diagram of LIG-MSCs device architecture. FIGS. 16D-E provideCV curves of LIG-MSCs at scan rates from 20 to 10,000 mV·s⁻¹. FIG. 16Fprovides specific areal capacitance (C_(A)) calculated from CV curves asa function of scan rates. FIGS. 16G-H provide CC curves of LIG-MSCs atdischarge current densities (I_(D)) varied from 0.2 to 25 mA·cm⁻². FIG.16I provides C_(A) calculated from CC curves vs. I_(D). FIGS. 16J-Kprovide charge density distribution of the states within a voltagewindow (−0.1, 0.1) V for type I and II polycrystalline sheets. Thedefects at the grain boundaries are shadowed, and numbers show themisorientation angle between the grains. FIG. 16L provides a carbonlayer fully composed of pentagons and heptagons (pentaheptite). FIG. 16Nprovides calculated quantum capacitance (defined in Example 1) ofperfect and polycrystalline/disordered graphene layers.

FIG. 17 provides electrochemical characterizations of LIG-MSCs obtainedfrom PI and PEI using different laser powers in 1 M H₂SO₄. FIG. 17A is acomparison of CV curves of LIG-MSCs obtained from PI at scan rates of100 mV·s⁻¹. FIG. 17B provides a specific areal capacitances of LIG-MSCsobtained from PI, calculated from CC curves at current densities of 0.2mA·cm⁻², as a function of the laser power. FIG. 17C provides acomparison of CV curves of LIG-MSCs obtained from PEI at scan rates of 1V·s⁻¹. FIG. 17D provides specific areal capacitances of LIG-MSCsobtained from PEI, calculated from CC curves at a current density of 0.2mA·cm⁻², as a function of the laser power. Compared to PEI derivedLIG-MSCs, LIG-MSCs obtained from PI have ˜10× higher capacitancesprepared at the same laser powers.

FIG. 18 provides impedance spectroscopy of LIG-MSCs obtained from PIusing a laser power of 4.8 W in 1 M H₂SO₄. Equivalent series resistanceis as low as 7Ω obtained at a high frequency range.

FIG. 19 provides electrochemical characterizations of LIG-MSCs obtainedwith a laser power of 4.8 W in BMIM-BF₄. FIGS. 19A-B provide CV curvesof LIG-MSCs at scan rates from 20 mV·s⁻¹ to 5 V·s⁻¹. FIG. 19C providesspecific areal capacitances vs. scan rates. FIGS. 19D-E provide CCcurves of LIG-MSCs at discharge current densities from 0.1 mA/cm² to 7mA/cm². The voltage drop is shown graphically in FIG. 19E. FIG. 19Fshows a specific areal capacitances vs. discharge current densities.

FIG. 20 provides a comparison of volumetric capacitances that arecalculated from CC curves of LIG-MSCs in aqueous electrolyte and ionicliquid (IL). FIG. 20A provides specific volumetric capacitances as afunction of discharge current densities in 1 M H₂SO₄. FIG. 20B providesspecific volumetric capacitances as a function of discharge currentdensities in BMIM-BF₄.

FIG. 21 provides electrochemical performance of LIG-MSCs inseries/parallel combinations. Electrolyte for devices in FIGS. 21A-B is1 M H₂SO₄, and for devices in FIG. 21C is BMIM-BF₄. FIG. 21A provides CCcurves of two tandem LIG-MSCs connected in series with the samedischarge current density of 1 mA/cm². The operation potential window isdoubled in serial configuration. FIG. 21B provides CC curves of twotandem LIG-MSCs in parallel assembly with the same discharge currentdensity of 1 mA/cm². In this configuration, capacitance is almostdoubled. FIG. 21C provides CC curves of single LIG-MSCs and 10 parallelLIG-MSCs at discharge current densities of 1 mA/cm² and 10 mA/cm²,respectively. Current density increases by a factor of 10 with 10parallel single devices. Inset is a lighted LED powered by 10 parallelLIG-MSCs.

FIG. 22 provides a comparison Ragone plots of different energy storagedevices. FIG. 22A provides a specific volumetric energy and powerdensities of energy storage devices. FIG. 22B provides a specific arealenergy and power densities of LIG-MSCs and LSG-MSCs. LSG, battery and Alelectrolytic capacitor data were reproduced from the literature forcomparison.

FIG. 23 provides capacity retention of LIG-MSCs constructed with LIG-4.8W in 1 M H₂SO₄ and ionic liquid (BMIM-BF₄). FIG. 23A shows thatcapacitance, calculated from CV curves at a scan rate of 100 mV·s⁻¹,increases to 114% of the original value after 2750 cycles, and thenretains almost the same value after 9000 cycles. FIG. 23B shows thatcapacitance, calculated from CV curves at a scan rate of 100 mV·s⁻¹,degrades to 95.5% of original value after 1000 cycles, and thenstabilizes at 93.5% after 7000 cycles.

FIG. 24 provides CV curves of LIG-MSCs obtained with laser power of 4.8W in IM H₂SO₄ (FIG. 24A) and BMIM-BF₄ (FIG. 24B). The curves wereobtained at a sweep rate of 100 mV·s⁻¹ after every 1000 cycles.

FIG. 25 provides atomic structures of the calculated polycrystallinegraphene sheets. The arrows indicate the unit cell, and the grainboundary regions are shaded. Numbers show two types of misorientationangles (21.8° and 32.2°) between grains.

FIG. 26 provides data and images relating to the formation ofboron-doped LIG (B-LIG) and fabrication of MSCs containing the B-LIGs(B-LIG-MSC). FIG. 26A provides a synthetic scheme for the preparation ofB-LIG and fabrication of the B-LIG-MSC. FIG. 26B provides a scheme ofthe dehydration reaction from PAA to a PI film during a curing process.FIG. 26C provides SEM images of 5B-LIG. The inset in (FIG. 26C) is thecross sectional SEM image of 5B-LIG on a PI sheet. FIG. 26D shows a TEMimage of 5B-LIG. FIG. 26E shows an HRTEM image of 5B-LIG.

FIG. 27 is shows photographs of a PAA solution with 5 wt % of H₃BO₃(FIG. 27A) and patterned B-LIG on the PI/H₃BO₃ sheet after laserinduction (FIG. 27B).

FIG. 28 shows SEM images of LIG materials with different boron loadings,including 0B-LIG (FIG. 28A), 1B-LIG (FIG. 28B), 2B-LIG (FIG. 28C), and8B-LIG (FIG. 28D).

FIG. 29 provides TEM and HRTEM images of LIG materials with differentboron loadings, including 0B-LIG (FIGS. 29A and 29E), 1B-LIG (FIGS. 29Band 29F), 2B-LIG (FIGS. 29C and 29G), and 8B-LIG (FIGS. 29D and 29H).

FIG. 30 provides data relating to the characterization of 5B-LIGmaterials. FIG. 30A shows the Raman spectrum of 5B-LIG. FIG. 30B showsthe XRD pattern of 5B-LIG. FIG. 30C shows the TGA curve of 5B-LIG and5B-PI at 5° C./min under argon. FIG. 30D shows the pore sizedistribution of 5B-LIG.

FIG. 31 shows the BET measurement of B-LIG materials. The calculatedsurface area is 191 m²/g.

FIG. 32 shows XPS survey spectra for 5B-PI (FIG. 32A) and 5B-LIG (FIG.32B).

FIG. 33 shows XPS spectra of 5B-LIG and PI/H₃BO₃ sheets. FIG. 33A showsthe C1s spectrum. FIG. 33B shows the O1s spectrum. FIG. 33C shows theB1s spectrum. FIG. 33D shows the N1s spectrum.

FIG. 34 provides an electrochemical performance comparison of LIG-MSCswith different H₃BO₃ loadings. FIG. 34A provides a schematic of aB-LIG-MSC device and the digital photograph of a fully-fabricated deviceunder bending. FIG. 34B provides CV curves of MSCs from PI derived LIG,PAA derived LIG and PAA/H₃BO₃ derived LIG at a scan rate of 0.1 V/s.FIG. 34C provides CC curves of MSCs from PI derived LIG and PAA/H₃BO₃derived LIG at a current density of 1.0 mA/cm². FIG. 34D provides CVcurves of LIG-MSC and B-LIG-MSC with different H₃BO₃ loadings. The scanrate is set at 0.1 V/s. FIG. 34E provides Galvanostatic CC curves ofLIG-MSC and B-LIG-MSC with different H₃BO₃ loadings. The current densityis set at 1 mA/cm². FIG. 34F provides a comparison of calculated C_(A)from LIG-MSC and B-LIG-MSC with different H₃BO₃ loadings. The currentdensity is at 1 mA/cm². FIG. 34G provides a chart of LIG-MSC capacitanceas a function of current. An expanded schematic of FIG. 34A is alsoprovided.

FIG. 35 provides data relating to the electrochemical performance of5B-LIG-MSC. FIG. 35A shows CV curves of 5B-LIG-MSC at scan rates of 10,20, 50 and 100 mV/s. FIG. 35B shows galvanostatic CC curves of5B-LIG-MSC at current densities of 0.1, 0.2 and 0.5 mA/cm². FIG. 35Cshows specific C_(A) of 5B-LIG-MSC calculated from CC curves as afunction of current density. FIG. 35D shows cyclability testing of5B-LIG-MSC. The charge-discharge cycles are performed at a currentdensity of 1.0 mA/cm². FIG. 35E shows a digital photograph of a bent5B-LIG-MSC at a bending radius of 10 mm. FIG. 35F shows capacitanceretention of 5B-LIG-MSC at different bending radii. FIG. 35G shows bentcyclability testing of flexible 5B-LIG-MSC at a fixed bending radius of˜10 mm. The C_(p) is calculated from discharge runtime at a currentdensity of 1.0 mA/cm². FIG. 35H shows CV curves of the 5B-LIG-MSC atdifferent bending cycles in (FIG. 35G) at a scan rate of 50 mV/s. FIG.35I shows volumetric Ragone plot of 5B-LIG-MSC and LIG-MSC.

FIG. 36 provides additional electrochemical performance of 5B-LIG-MSC.FIG. 36A provides CV curves of 5B-LIG-MSC at scan rates of 0.2, 0.5, 1.0and 2.0 V/s. FIG. 36B provides CV curves of 5B-LIG-MSC at scan rates of5, 10, 15 and 20 V/s. FIG. 36C provides galvanostatic CC curves of5B-LIG-MSC at current densities of 1.0, 2.0 and 5.0 mA/cm². FIG. 36Dprovides galvanostatic CC curves of 5B-LIG-MSC at current densities of10, 20 and 30 mA/cm².

FIG. 37 provides impedance performances of LIG-MSC and 5B-LIG-MSC. Thetesting frequency is ranging from 10⁶ Hz to 0.01 Hz. This typicalNyquist plot shows a small semicircle for both devices at a highfrequency region, corresponding to a fast ionic transport and lowexternal resistance of devices. At the lower frequency region, theNyquist plot exhibits a linear part resulting from the interface betweenthe electrolyte and the electrode. This interface results in internalresistance of devices. From this Nyquist plot, Applicants can see that5B-LIG-MSC has both smaller external and internal resistances thanLIG-MSC. These results indicate faster ionic transport and betterelectrode-electrolyte interface in 5B-LIG-MSC.

FIG. 38 provides an areal Ragone plot of 5B-LIG-MSC and LIG-MSC.

FIG. 39 provides data and illustrations relating to the fabrication andcharacterization of LIG super capacitors (LIG-SCs). FIG. 39A is aschematic illustration showing the fabrication process for assembling asingle LIG-SC and stacked LIG-SC. FIG. 39B is an optical image of afully assembled single LIG-SC manually bent. FIG. 39C is across-sectional SEM image of a PI substrate with both sides laserinduced to form graphene. FIG. 39D is an SEM image of the LIG filmsshowing a porous 3D network. FIG. 39E is a TEM image of a LIG thin filmshowing nano-sized wrinkles and ripples. The inset is a HRTEM image of aLIG nanosheet showing numerous graphene edges

FIG. 40 is a photograph of a half-side LIG electrode for LIG-SCs.

FIG. 41 is an illustration of the fabrication process of a solid-stateLIG-MSC.

FIG. 42 provides data relating to an electrochemical performance of asingle LIG-SC. FIG. 42A provides CV curves of LIG-SCs at scan rates of5, 10, 20 and 50 mV/s. FIG. 42B provides Galvanostatic CC curves ofLIG-SCs at current densities of 0.02, 0.05, 0.10 and 0.20 mA/cm². FIG.42C provides specific areal capacitances calculated from CC curves as afunction of current density. FIG. 42D provides cyclability testing ofLIG-SCs with a CC current density of 0.8 mA/cm².

FIG. 43 provides data relating to the characterization of LIGs. FIG. 43Aprovides a Raman spectrum of LIGs. FIG. 43B provides an XRD spectrum ofLIGs.

FIG. 44 provides a TGA plot of LIG and PI substrates under argon. PIstarts to decompose at ˜550° C., while LIG remains stable up to 900° C.The LIG for this analysis was removed from the underlying PI film asdescribed in the Methods.

FIG. 45 provides a BET measurement of LIGs. FIG. 45A provides nitrogenadsorption/desorption curves of LIGs. The calculated surface area is 330m²/g. FIG. 45B provides pore size distributions of LIGs.

FIG. 46 provides additional electrochemical performance of a flat,single LIG-SC. FIG. 46A provides CV curves of LIG-SCs at scan rates of0.1, 0.2, 0.5 and 1.0 V/s. FIG. 46B provides Galvanostatic CC curves ofLIG-SCs at current densities of 0.5, 1.0 and 2.0 mA/cm².

FIG. 47 provides electrochemical performance of LIG-SCs under bending.FIG. 47A provides CV curves of LIG-SC at varying bending radii. The scanrate was 0.02 V/s. FIG. 47B provides capacity retention at differentbending radius. Capacitance retention was calculated from CC curves at acurrent density of 0.05 mA/cm². FIG. 47C provides cyclability testing offlexible LIG-SCs. Capacitance retention was calculated from CC curves ata current density of 0.4 mA/cm².

FIG. 48 provides electrochemical performances of stacked LIG-SCs inseries and parallel circuits. FIG. 48A provides an illustration of astacked series LIG-SC and its corresponding circuit diagram. FIG. 48Bprovides an illustration of a stacked parallel LIG-SC and itscorresponding circuit diagram. FIG. 48C provides galvanostatic CC curvescomparing a single LIG-SC to a stacked series LIG-SC at a currentdensity of 0.5 mA/cm². FIG. 48D provides galvanostatic CC curvescomparing a single LIG-SC to a stacked parallel LIG-SC at a currentdensity of 0.5 mA/cm². FIG. 48E provides a cyclability testing of aflexible stacked series LIG-SC at a current density of 0.5 mA/cm². Insetshows the initial CV curves (black) and the 4000th CV curve (red) at ascan rate of 0.1 V/s. FIG. 48F shows a cyclability testing of aflexible, stacked parallel LIG-SC at a current density of 1.0 mA/cm².Inset shows the initial CV curves (black) and the 6000^(th) CV curve(red) at a scan rate of 0.1 V/s.

FIG. 49 provides electrochemical performances of stacked LIG-SCs inseries configurations. FIG. 49A provides CV curves of series LIG-SCs atscan rates of 5, 10, 20 and 50 mV/s. FIG. 49B provides galvanostaticcharge-discharge curves of series LIG-SCs at current densities of 0.1,0.2 and 0.5 mA/cm².

FIG. 50 provides electrochemical performance of stacked LIG-SCs inparallel. FIG. 50A provides CV curves of parallel LIG-SCs at scan rateof 10, 20, 50 and 100 mV/s. FIG. 50B provides galvanostaticcharge-discharge curves of parallel LIG-SCs at current densities of 0.1,0.2, 0.5 and 1.0 mA/cm². FIG. 50C provides specific areal capacitancecalculated from discharge runtime as a function of current density.

FIG. 51 provides electrochemical performances of LIG-MSC devices. FIG.51A provides an illustration of a flexible LIG-MSC. The inset is aphotograph of a LIG-MSC fixed at a bending radius of 12 mm. FIG. 51Bprovides CV curves of LIG-MSCs at scan rates of 10, 20, 50 and 100 mV/s.FIG. 51C provides Galvanostatic CC curves of LIG-MSCs at currentdensities of 0.1, 0.2, 0.5 and 1.0 mA/cm². FIG. 51D provides specificC_(A) of LIG-MSCs from aqueous 1 M H₂SO₄ and PVA/H₂SO₄ calculated fromCC curves as a function of the current density. FIG. 51E providescapacity retention of LIG-MSC at different bending radii. Capacitanceretention was calculated from CC curves at a current density of 0.5mA/cm². FIG. 51F provides cyclability testing of flexible LIG-MSCs.Capacitance retention was calculated from CC curves at a current densityof 0.5 mA/cm².

FIG. 52 provides additional data relating to the electrochemicalperformance of flat LIG-MSC devices. FIG. 52A provides CV curves ofLIG-MSCs at scan rates of 0.2, 0.5, 1.0 and 2.0 V/s. FIG. 52B providesCV curves of LIG-MSCs at scan rates of 5.0, 10 and 20 V/s. FIG. 52Cprovides CC curves of LIG-MSCs at current densities of 2, 5, 10 and 20mA/cm².

FIG. 53 provides impedance performances of LIG-MSCs with aqueous 1 MH₂SO₄ and PVA/H₂SO₄ electrolyte. This typical Nyquist plot shows a smallsemicircle at a high frequency region that corresponds to the ionictransport which contributes to the external resistance of the device.The lower frequency region of the Nyquist plot exhibits linearity due tothe interaction between the electrolyte and electrode. This interfaceresults in internal resistance of the device. From this Nyquist plot,Applicants can see that LIG-MSC in PVA/H₂SO₄ has both a smaller externaland internal resistance than those in aqueous H₂SO₄. These resultsindicate faster ionic transport and better electrode-electrolyteinterface in LIG-MSCs using PVA/H₂SO₄.

FIG. 54 provides data relating to the cyclability test of LIG-MSCs. TheCC current density was set at 1.0 mA/cm². The capacitance remained >90%after 8000 cycles.

FIG. 55 provides electrochemical performance of LIG-MSCs in series orparallel combinations. FIG. 55A provides CC curves of two tandemLIG-MSCs connected in series with the same discharge current density.The operation potential window is doubled in series configuration. FIG.55B provides CC curves of two tandem LIG-MSCs in parallel assembly withthe same discharge current density. In this configuration capacitance isalmost doubled. Both tandem devices and the single device were appliedwith the same discharge/charge current density.

FIG. 56 provides CV curves of the flexible LIG-MSC at different bendingradius. The scan rate is set at 0.1 V/s.

FIG. 57 provides Ragone plots of single LIG-SC, LIG-MSC and commercialenergy storage devices.

FIG. 58 provides Ragone plots of single LIG-SC and LIG-MSC in specificareal energy and power densities.

FIG. 59 provides an absorption spectrum of a polyimide film. The fourvertical lines represent where a tunable CO₂ laser could specificallyaddress key lines of polymer absorbance to induce graphene formation.

FIG. 60 is a drawing showing the use of visible lasers and an option ofcoupling into a controlled atmosphere chamber with an optical fiber.

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are illustrative and explanatory, andare not restrictive of the subject matter, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise.

The section headings used herein are for organizational purposes and arenot to be construed as limiting the subject matter described. Alldocuments, or portions of documents, cited in this application,including, but not limited to, patents, patent applications, articles,books, and treatises, are hereby expressly incorporated herein byreference in their entirety for any purpose. In the event that one ormore of the incorporated literature and similar materials defines a termin a manner that contradicts the definition of that term in thisapplication, this application controls.

Over the past decade, graphene based nanomaterials have been widelystudied due to their unique physical and chemical properties. Throughsynthesis and engineering design, graphene can have porous and3-dimensional (3D) structures, leading to a wide range of applicationsfrom composite fillers to energy storage devices. Despite the tremendousadvances, current synthesis methods of porous graphene require eitherhigh temperature processing or multi-stepped chemical synthesis routes,thereby lessening their wide-spread commercial potential. Therefore,straightforward synthesis, and especially patterning, of graphene basednanomaterials in a scalable approach is still a technologicallyimportant goal in achieving commercialized microscale energy storagedevices.

For instance, glassy carbon has been produced from insulating polyimidevia pulsed ultraviolet (UV) laser treatment. However, to Applicants'knowledge, the detailed structural study of the obtained materials,especially at the near-atomic level; the correlation of the materials'structures to their electrochemical performances; and the formation ofgraphene by this route have not been disclosed.

Moreover, the technique of laser scribing insulating polymers for thefabrication of electronic devices (e.g., energy storage devices, such asmicrosupercapacitors or MSCs) has not yet been demonstrated. In fact,the cost-effective synthesis and patterning of carbon nanomaterials forincorporation into electronic devices has been a challenge.

Energy storage systems, such as supercapacitors (SCs) and lithium ionbatteries (LIBs), have been widely studied over the past few years inorder to meet the rapidly growing demand for highly efficient energydevices. Intense ongoing research has focused on miniaturized portableelectronics which require small size, light weight and mechanicalflexibility while maintaining high energy and power densities. Recentprogress in microfabrication technologies has allowed for the in-planemanufacturing of microsupercapacitors (MSCs) made using lithographictechniques that would be suitable for integrated circuits. However, suchfabrication methods may not be cost-effective for projected commoditytargets, slowing their scalability and commercialization.

Graphene-based materials have been extensively studied as activeelectrodes in MSCs due to their unique structure and their extraordinarymechanical and electrical properties. To further improve theirperformance, many methods have been employed to modulate the electronicband structure of the graphene-derived materials. Among them, dopingwith heteroatoms (such as boron, nitrogen, phosphorus, and sulfur) hasbeen shown to be an effective way to tailor the electrochemicalproperties of graphene-derived conductive materials and to enhance theircapacitive performances. Particularly, substitutions of carbon withboron in the graphene lattice shifts the Fermi level toward the valanceband, thereby enhancing charge storage and transfer within the dopedgraphene structure. Moreover, the presence of boron dopants in graphenecontributes to a space-charge-layer capacitance and/orpseudocapacitance, further increasing the apparent capacitance. However,current synthesis processes for obtaining graphene (includingboron-doped graphene) require either multi-step chemical reactions orhigh-temperature and high-vacuum environments, making them unsuitablefor low-cost commodity-driven applications.

For example, a recently developed method to make graphene uses laserscribing of graphene oxide (GO) films, where GO is then reduced,patterned, and fabricated to make graphene-based devices that exhibitoptimal electrochemical performance. Unfortunately, the synthesis of GOand its subsequent formation into films is still far fromcommercialization in bulk quantities. Furthermore, recent studies haveshown that GO decomposes over time, which can lead to significantcurrent leakage or device changes within GO-derived devices.

As such, a need exists for more effective methods of developinggraphene-based materials for various electronic applications. Variousembodiments of the present disclosure address this need.

In some embodiments, the present disclosure pertains to methods ofproducing a graphene material. In some embodiments illustrated in FIG.1, the methods of the present disclosure include exposing a polymer to alaser source (step 10) to result in the formation of a graphene that isderived from the polymer (step 12). In some embodiments, the methods ofthe present disclosure also include a step of incorporating the formedgraphene material into an electronic device (step 14). In someembodiments, the methods of the present disclosure also include a stepof separating the formed graphene from the polymer to form an isolatedgraphene (step 13), and incorporating the isolated graphene into anelectronic device (step 14).

Additional embodiments of the present disclosure pertain to the graphenematerials that are formed by the methods of the present disclosure. Anexample of a graphene material of the present disclosure is shown inFIG. 1B. In this example, graphene material 20 includes polymer 22 withfirst surface 24. Graphene material 20 also includes graphene 26 derivedfrom polymer 22. Graphene 26 in this example has an interdigitatedpattern on surface 24 of polymer 22.

In some embodiments, the graphene materials and the isolated graphenesof the present disclosure serve as a component of an electronic device.In further embodiments, the present disclosure pertains to electronicdevices that contain the graphene materials and isolated graphenes ofthe present disclosure.

An example of an electronic device of the present disclosure is shown inFIG. 1C. In this example, electronic device 30 includes polymer 32 andgraphene 36 derived from polymer 32. Graphene 36 in this example has aninterdigitated pattern and serves as an electrode in electronic device30. As described in more detail herein, electronic device 30 alsoincludes tape 34, paint 37, and electrolyte 38. In this example,electronic device 30 can serve as an in-plane micro supercapacitor.

Another example of an electronic device of the present disclosure isshown in FIG. 1D. In this example, electronic device 40 includes a stackof graphene materials 42, 44 and 46. Graphene material 42 includespolymer 50. Graphene material 42 also includes graphenes 48 and 52derived from polymer 50. Graphenes 48 and 52 are on opposite sides ofpolymer 50. Likewise, graphene material 44 includes polymer 58 andgraphenes 56 and 60 derived from polymer 58. Graphenes 56 and 60 are onopposite sides of polymer 58. In addition, graphene material 46 includespolymer 66 and graphene 64 derived from polymer 66. Graphene materials42 and 44 are separated from one another by solid electrolyte 54.Likewise, graphene materials 44 and 46 are separated from one another bysolid electrolyte 62. In this example, electronic device 40 can serve asa stacked supercapacitor.

As set forth in more detail herein, various methods may be utilized toexpose various polymers to various laser sources to result in theformation of various types of graphenes. Various methods may also beutilized to separate the formed graphenes from the polymers. Variousmethods may also be utilized to incorporate the formed graphenematerials and isolated graphenes of the present disclosure into variouselectronic devices.

Laser Sources

The polymers of the present disclosure may be exposed to various lasersources. For instance, in some embodiments, the laser source includes,without limitation, a solid state laser source, a gas phase lasersource, an infrared laser source, a CO₂ laser source, a UV laser source,a visible laser source, a fiber laser source, near-field scanningoptical microscopy laser source, and combinations thereof. In someembodiments, the laser source is a UV laser source. In some embodiments,the laser source is a CO₂ laser source. Additional laser sources canalso be envisioned.

The laser sources of the present disclosure can have variouswavelengths. For instance, in some embodiments, the laser source has awavelength ranging from about 1 nm to about 100 μm. In some embodiments,the laser source has a wavelength ranging from about 20 nm to about 100μm. In some embodiments, the laser source has a wavelength ranging fromabout 10 nm to about 400 nm. In some embodiments, the laser source has awavelength ranging from about 400 nm to about 800 nm. In someembodiments, the laser source has a wavelength ranging from about 1 μmto about 100 μm. In some embodiments, the laser source has a wavelengthranging from about 1 μm to about 50 μm. In some embodiments, the lasersource has a wavelength ranging from about 1 μm to about 20 μm. In someembodiments, the laser source has a wavelength ranging from about 5 μmto about 15 μm. In some embodiments, the laser source has a wavelengthof about 10 μm. Additional wavelengths can also be envisioned.

In some embodiments, the laser sources of the present disclosure have awavelength that matches an absorbance band in the absorbance spectrum ofa polymer that is being exposed to the laser source. In suchembodiments, a more efficient energy transfer from the laser source tothe polymer can occur, thereby resulting in conversion of the polymer tographene in the laser-exposed regions. In some embodiments, a polymer ischosen such that an absorbance band in the polymer matches theexcitation wavelength of the laser source.

The laser sources of the present disclosure can also have various powerranges. For instance, in some embodiments, the laser source has a powerranging from about 1 W to about 10 W. In some embodiments, the lasersource has a power ranging from about 1 W to about 6 W. In someembodiments, the laser source has a power ranging from about 2 W toabout 5 W. In some embodiments, the laser source has a power rangingfrom about 2 W to about 4 W. In some embodiments, the laser source has apower ranging from about 2 W to about 3 W. In some embodiments, thelaser source has powers ranging from about 2.4 W to about 5.4 W.Additional power ranges can also be envisioned. In some embodiments, thelaser sources of the present disclosure have power ranges that can varybased upon the absorbance of the polymer at a chosen laser wavelength.

The laser sources of the present disclosure can also have various pulsewidths. For instance, in some embodiments, the laser sources of thepresent disclosure have pulse widths that are in the range offemtoseconds, nanoseconds, or milliseconds. In some embodiments, thelaser sources of the present disclosure have pulse widths that rangefrom about 1 femtosecond to about 1 ms. In some embodiments, the lasersources of the present disclosure have pulse widths that range fromabout 1 femtosecond to about 1 ns. In some embodiments, the lasersources of the present disclosure have pulse widths that range fromabout 1 μs to about 1 ms. In some embodiments, the laser sources of thepresent disclosure have pulse widths that range from about 1 μs to about100 μs. In some embodiments, the laser sources of the present disclosurehave pulse widths that range from about 10 μs to about 50 μs. In someembodiments, the laser sources of the present disclosure have pulsewidths of about 15 μs. Additional pulse widths can also be envisioned.

In some embodiments, the laser source is a CO₂ laser source with awavelength of about 10.6 μm. As set forth in more detail in the Examplesherein, Applicants have observed that the application of CO₂ lasersources to polymer surfaces (e.g., polyimides) at wavelengths of about10.6 μm provides porous graphenes with optimal electrical properties.

The use of additional laser sources at different wavelengths can also beenvisioned. For instance, in some embodiments, the polymers of thepresent disclosure may be exposed to a single laser source. In someembodiments, the polymers of the present disclosure may be exposed totwo or more laser sources. In some embodiments, the polymers of thepresent disclosure may be simultaneously exposed to two or more lasersources. In some embodiments, the two or more laser sources may have thesame or different wavelengths, power ranges, and pulse widths.

Exposure of a Polymer to a Laser Source

Various methods may be utilized to expose polymers to a laser source. Insome embodiments, the exposure occurs manually. In some embodiments, theexposure occurs automatically. For instance, in some embodiments, theexposure occurs automatically through computer-controlled mechanisms. Insome embodiments, the exposure occurs automatically through a computerpatterning system. In some embodiments, the exposure occursautomatically through automated processing lines. In some embodiments,the exposure occurs automatically through automated processing lineswith multiple laser sources. In some embodiments, the multiple lasersources could vary in wavelength or power to cause different degrees ofgraphene formation over different regions of the polymer.

In some embodiments, the exposure of polymers to a laser source includespulsed laser irradiation. In some embodiments, the exposure of polymersto a laser source includes continuous laser irradiation. In someembodiments, the exposure of polymers to a laser source includespatterning a surface of the polymer with the formed graphene. Forinstance, in some embodiments, the surface of the polymer is patternedinto interdigitated shapes.

In some embodiments, the exposure of a polymer to a laser sourceincludes a step of tuning one or more parameters of the laser source. Insome embodiments, the one or more tunable parameters of the laser sourceinclude, without limitation, laser wavelength, laser power, laser energydensity, laser pulse widths, gas environment, gas pressure, gas flowrate, and combinations thereof.

In some embodiments, the one or more parameters of a laser source aretuned according to one or more attributes of the exposed polymer. Insome embodiments, the one or more attributes of the exposed polymerinclude, without limitation, polymer type, polymer thickness, polymermorphology, polymer structure, polymer absorbance spectrum, a substrateupon which a polymer may be affixed, and combinations thereof.

In some embodiments, the one or more parameters of a laser source aretuned in order to maximize the absorption of the laser wavelength by thepolymer. For instance, in some embodiments, the laser wavelength of thelaser source is tuned to match an absorbance band of a polymer. In someembodiments, such tuning optimizes laser light absorbance by the polymerand results in optimal graphene formation upon laser-polymerinteraction. In some embodiments, the absorbance band of the polymercorresponds to the wavelength of the laser source.

In some embodiments, the one or more parameters of a laser source aretuned in order to control the penetration depth of the laser wavelengthby the polymer. In some embodiments, the penetration depth (orabsorption depth) of a laser source is maximized by tuning thewavelength of the laser source. As such, in some embodiments, a stronglyabsorbed wavelength can be focused on a polymer surface to create adesired form of graphene. Moreover, the availability to choose from manywavelengths can allow for selection of a wide range of penetrationdepths into a polymer or type of polymer by changing the wavelength ofthe laser source. This in turn allows for controlling the depth of theformed graphene and the type of polymer from which graphene can beformed. For instance, in some embodiments, the laser source can be tunedto create a narrow and shallow line of graphene on a surface of apolymer by using a well-focused laser at lower power ranges.

In some embodiments, the exposure of a polymer to a laser sourceincludes a step of tuning one or more parameters of the polymer. Forinstance, in some embodiments, a polymer's absorbance band can be tunedto match the excitation wavelength of a laser source. In someembodiments, the tuning occurs by modifying the structure of thepolymer. In some embodiments, the modification can ensure optimalgraphene formation upon laser-polymer interaction. In some embodiments,the absorbance band of a polymer can be modified to match the excitationwavelength of the laser source by adding a compound to the polymer thatabsorbs well at the excitation wavelength of the laser source.

In some embodiments, the exposure of a polymer to a laser source caninclude the utilization of optical microscopic techniques. In someembodiments, the microscopic techniques can be used to providenanometer-scaled patterns of graphene on the polymer surface. Forinstance, in some embodiments, near-field scanning optical microscopy(NSOM) can be used during the exposure of a surface of a polymer to alaser source to provide nanometer-scaled patterns of graphene on thepolymer surface. In some embodiments, the nanometer-scaled patterns ofgraphene on the polymer surface can have resolutions of about 20 nm.

Polymers

The laser sources of the present disclosure may be applied to varioustypes of polymers. For instance, in some embodiments, the polymers ofthe present disclosure include, without limitation, vinyl polymers,homopolymers, block co-polymers, carbonized polymers, aromatic polymers,cyclic polymers, polyimide (PI), polyetherimide (PEI), polyether etherketone (PEEK), and combinations thereof. In some embodiments, thepolymers of the present disclosure include polyimides.

In some embodiments, the polymers of the present disclosure may bechosen based on the chosen laser source. For instance, in someembodiments, a polymer with an absorbance wavelength may be exposed to alaser source with a matching laser excitation wavelength.

In some embodiments, the polymers of the present disclosure lackgraphite oxides. In some embodiments, the polymers of the presentdisclosure lack graphene oxides. In some embodiments, the polymers ofthe present disclosure include aromatic monomers. The use of additionalpolymers can also be envisioned.

The polymers of the present disclosure may also be modified in variousmanners. For instance, in some embodiments, the polymers of the presentdisclosure may include doped polymers. In some embodiments, the dopedpolymers of the present disclosure may be doped with one or moredopants. In some embodiments, the one or more dopants include, withoutlimitation, heteroatoms, metals, metal oxides, metal chalcogenides,metal nanoparticles, metal salts, organic additives, inorganicadditives, metal organic compounds, and combinations thereof. In someembodiments, the one or more dopants include, without limitation,molybdenum, tungsten, iron, cobalt, manganese, magnesium, copper, gold,palladium, nickel, platinum, ruthenium, metal chalcogenides, metalhalides, metal acetates, metal acetoacetonates, related salts thereof,and combinations thereof.

In some embodiments, the polymers of the present disclosure may be dopedwith one or more metal salts. In some embodiments, the metal saltsinclude, without limitation, iron acetylacetonate, cobaltacetylacetonate, molyddenyl acetylacetonate, nickel acetylacetonate,iron chloride, cobalt chloride, and combinations thereof.

In some embodiments, the doped polymers of the present disclosureinclude heteroatom-doped polymers. In some embodiments, theheteroatom-doped polymers of the present disclosure include, withoutlimitation, boron-doped polymers, nitrogen-doped polymers,phosphorus-doped polymers, sulfur-doped polymers, and combinationsthereof. In some embodiments, the heteroatom-doped polymers of thepresent disclosure include boron-doped polymers. In some embodiments,the doped polymers of the present disclosure are in the form of polymercomposites.

The dopants that are associated with the doped polymers of the presentdisclosure can have various shapes. For instance, in some embodiments,the dopants can be in the form of nanostructures. In some embodiments,the nanostructures can include, without limitation, nanoparticles,nanowires, nanotubes, and combinations thereof. Additional dopantstructures can also be envisioned.

In some embodiments, the polymers of the present disclosure includecarbonized polymers. In some embodiments, the carbonized polymersinclude glassy or amorphous carbons. In some embodiments, the polymersof the present disclosure are carbonized by annealing at hightemperatures (e.g., temperatures ranging from about 500° C. to about2,000° C.).

In some embodiments, the polymers of the present disclosure includechemically treated polymers. For instance, in some embodiments, thepolymers of the present disclosure are chemically treated in order toenhance their surface areas. In some embodiments, the polymers of thepresent disclosure are thermally treated with a base, such as potassiumhydroxide.

The polymers of the present disclosure can have various shapes. Forinstance, in some embodiments, the polymers of the present disclosureare in the form of a sheet or a film, such as a flat sheet or film. Insome embodiments, the polymers of the present disclosure includecommercially available polyimide (PI) films. In some embodiments, thepolymers of the present disclosure are in the form of a powder. In someembodiments, the polymers of the present disclosure are in the form ofpellets. In some embodiments, the polymers of the present disclosure arein the form of a coupon. In some embodiments, the polymers of thepresent disclosure are in the form of a block. In some embodiments, thepolymers of the present disclosure are in the form of a fabricated part,such an aircraft wing. In some embodiments, the polymers of the presentdisclosure are in the form of an electronics circuit substrate. In someembodiments, the polymers of the present disclosure are in the form of amonolithic block. In some embodiments, the polymers of the presentdisclosure are in the form of a composite.

In some embodiments, the polymers of the present disclosure are in theform of squares, circles, rectangles, triangles, trapezoids, spheres,pellets, and other similar shapes. In some embodiments, the polymers ofthe present disclosure are in the form of rectangles. In someembodiments, the polymers of the present disclosure are in the form offilms. In some embodiments, the polymers of the present disclosure arein the form of rolls of films.

The polymers of the present disclosure can also have various sizes. Forinstance, in some embodiments, the polymers of the present disclosurehave lengths or widths that range from about 100 m to about 1 mm. Insome embodiments, the polymers of the present disclosure have lengths orwidths that range from about 100 cm to about 10 mm. In some embodiments,the polymers of the present disclosure have lengths or widths that rangefrom about 10 cm to about 1 cm. In some embodiments, the polymers of thepresent disclosure are in the form of rolls of films that are 100 m longand 1 m wide.

The polymers of the present disclosure can also have variousthicknesses. For instance, in some embodiments, the polymers of thepresent disclosure have thicknesses that range from about 10 cm to about1 μm. In some embodiments, the polymers of the present disclosure havethicknesses that range from about 1 cm to about 1 mm. In someembodiments, the polymers of the present disclosure have thicknessesthat range from about 0.3 nm to about 1 cm. In some embodiments, thepolymers of the present disclosure have thicknesses that range fromabout 10 mm to about 1 mm.

The polymers of the present disclosure can also have various properties.For instance, in some embodiments, the polymers of the presentdisclosure are optically transparent. In some embodiments, the polymersof the present disclosure are rigid. In some embodiments, the polymersof the present disclosure are flexible. In some embodiments, thepolymers of the present disclosure are thermally stable (over 500° C.).

Graphene Formation

Graphenes may form from various polymers in various manners. Forinstance, in some embodiments, the exposing of a polymer to a lasersource includes exposing a surface of a polymer to a laser source. Insome embodiments, the exposing results in formation of the graphene onthe surface of the polymer.

Graphene can form on surfaces of polymers in various manners. Forinstance, in some embodiments, the graphenes form a pattern on a surfaceof the polymer. In some embodiments, the graphene becomes embedded withthe polymer. In some embodiments, the graphene forms on an outsidesurface of the polymer.

In some embodiments, the polymer includes a first surface and a secondsurface. In some embodiments, the first surface is exposed to the lasersource. As a result, the graphene forms on the first surface of thepolymer. In some embodiments, the first surface and the second surfaceof the polymer are exposed to the laser source. As a result, thegraphene forms on the first surface and the second surface of thepolymer. In some embodiments, the first surface and the second surfaceare on opposite sides of the polymer. As a result, the graphene can formon opposite sides of the polymer in some embodiments.

In some embodiments, the exposing of a polymer to a laser source resultsin conversion of the entire polymer to graphene (e.g., embodiments wherethe polymer is in powder form). In some embodiments, the formed graphenematerial consists essentially of the graphene derived from the polymer.

In some embodiments, the graphene forms in a three-dimensional patternfrom a polymer. As such, in some embodiments, the methods of the presentdisclosure can be utilized for the three-dimensional printing ofgraphene.

Without being bound by theory, it is envisioned that graphene can formfrom polymers by various mechanisms. For instance, in some embodiments,graphene forms by conversion of sp³-carbon atoms of polymers tosp²-carbon atoms. In some embodiments, graphene forms by photothermalconversion. In some embodiments, graphene is formed by photochemicalconversion. In some embodiments, graphene is formed by bothphotochemical and photothermal conversion.

In some embodiments, graphene forms by extrusion of one or moreelements. In some embodiments, the one or more elements can include,without limitation, hydrogen, oxygen, nitrogen, sulfur, and combinationsthereof.

Separation of Formed Graphenes from Polymers

In some embodiments, the methods of the present disclosure also includea step of separating the formed graphenes from the polymer. Theseparated graphenes are referred to herein as isolated graphenes.

Various methods may be utilized to separate formed graphenes frompolymers. In some embodiments, separating occurs chemically, such as bydissolving the polymer. In some embodiments, separating occursmechanically, such as by mechanically stripping the graphene from thepolymer. In some embodiments, separating occurs by scraping the formedgraphene from a surface of a polymer. Additional methods by which toseparate formed graphenes from polymers can also be envisioned.

Formed Graphenes

The methods of the present disclosure may be utilized to form varioustypes of graphenes. As set forth previously, the formed graphenes may beassociated with or separated from polymers.

In some embodiments, the graphenes of the present disclosures include,without limitation, single-layered graphene, multi-layered graphene,double-layered graphene, triple-layered graphene, doped graphene, porousgraphene, unfunctionalized graphene, pristine graphene, functionalizedgraphene, turbostratic graphene, oxidized graphene, graphite, graphenecoated with metal nanoparticles, metal particles coated with graphene,graphene metal carbides, graphene metal oxides, graphene metalchalcogenides, and combinations thereof. In some embodiments, thegraphenes of the present disclosure lack graphene oxides.

In some embodiments, the graphenes of the present disclosure includesporous graphene. In some embodiments, the porous graphenes includemesoporous graphenes, microporous graphenes, and combinations thereof.In some embodiments, the pores in the porous graphenes include diametersbetween about 1 nanometer to about 5 micrometers. In some embodiments,the pores include mesopores with diameters of less than about 50 nm. Insome embodiments, the pores include mesopores with diameters of lessthan about 9 nm. In some embodiments, the pores include mesopores withdiameters between about 1 μm and about 500 μm. In some embodiments, thepores include mesopores with diameters between about 5 nm and about 10nm. In some embodiments, the pores include mesopores with diametersbetween about 1 μm and about 500 μm. In some embodiments, the poresinclude micropores with diameters of less than about 2 nm. In someembodiments, the pores include micropores with diameters that range fromabout 1 nm to about 1 μm. Additional pore diameters can also beenvisioned.

In some embodiments, the graphenes of the present disclosure includedoped graphene. In some embodiments, the doped graphenes are doped withone or more dopants. In some embodiments, the dopants include, withoutlimitation, heteroatoms, metals, metal oxides, metal chalcogenides,metal nanoparticles, metal salts, organic additives, inorganicadditives, metal organic compounds, and combinations thereof.

In some embodiments, the doped graphenes include, without limitation,heteroatom-doped graphenes. In some embodiments, the heteroatom-dopedgraphenes of the present disclosure include, without limitation,boron-doped graphenes, nitrogen-doped graphenes, phosphorus-dopedgraphenes, sulfur-doped graphenes, silicon-doped graphenes, andcombinations thereof. In some embodiments, the heteroatom-dopedgraphenes of the present disclosure include boron-doped graphenes. Insome embodiments, the heteroatom-doped graphenes of the presentdisclosure include boron-doped porous graphenes.

In some embodiments, the dopants that are associated with dopedgraphenes of the present disclosure are in the form of heteroatomcarbides. In some embodiments, the heteroatom carbides include, withoutlimitation, boron carbides, boron-nitrogen carbides, silicon-carbides,and combinations thereof.

In some embodiments, the dopants of the doped graphenes of the presentdisclosure are in the form of nanoparticles. In some embodiments, thenanoparticles are coated on the graphene. In some embodiments, thenanoparticles include, without limitation, metal oxides, metal carbides,metal chalcogenides, and transition metal dichalcogenides. In someembodiments, the metal oxides include, without limitation, iron oxides,cobalt oxides, nickel oxides, molybdenum oxides, and copper oxides. Insome embodiments, the metal carbides include, without limitation, ironcarbides, tungsten carbides, nickel carbides, manganese carbides, cobaltcarbides, and molybdenum carbides. In some embodiments, the transitionmetal dichalcogenides include, without limitation, tungsten disulfide,molybdenum disulfide, and molybdenum diselenide.

The graphenes of the present disclosure can have various surface areas.For instance, in some embodiments, the graphenes of the presentdisclosure have surface areas ranging from about 100 m²/g to about 3,000m²/g. In some embodiments, the graphenes of the present disclosure havesurface areas ranging from about 500 m²/g to about 2800 m²/g. In someembodiments, the graphenes of the present disclosure have surface areasranging from about 100 m²/g to about 400 m²/g. In some embodiments, thegraphenes of the present disclosure have surface areas ranging fromabout 150 m²/g to about 350 m²/g.

The graphenes (e.g., porous graphene layers) of the present disclosurecan have various thicknesses. For instance, in some embodiments, thegraphenes of the present disclosure have thicknesses that range fromabout 0.3 nm to about 1 cm. In some embodiments, the graphenes of thepresent disclosure have thicknesses that range from about 0.3 nm toabout 50 μm. In some embodiments, the graphenes of the presentdisclosure have a thickness of about 25 μm.

The graphenes of the present disclosure can also have various shapes.For instance, in some embodiments, the graphenes of the presentdisclosure are in the form of flakes. In some embodiments, the graphenesof the present disclosure are highly wrinkled. In some embodiments, thegraphenes of the present disclosure have ripple-like wrinkledstructures.

In some embodiments, the graphenes of the present disclosure have athree-dimensional network. For instance, in some embodiments, thegraphenes of the present disclosure are in the shape of a foam withporous structures.

In some embodiments, the graphenes of the present disclosure have anordered porous morphology. In some embodiments, the graphenes of thepresent disclosure are in polycrystalline form. In some embodiments, thegraphenes of the present disclosure are in ultra-polycrystalline form.In some embodiments, the graphenes of the present disclosure containgrain boundaries. In some embodiments, the graphenes of the presentdisclosure include a polycrystalline lattice. In some embodiments, thepolycrystalline lattice may include ring structures. In someembodiments, the ring structures include, without limitation, hexagons,heptagons, pentagons, and combinations thereof. In some embodiments, thegraphenes of the present disclosure have a hexagonal crystal structure.In some embodiments, the graphenes of the present disclosure haveheptagon-pentagon pairs that comprise 20% to 80% of the surfacestructure.

In some embodiments, the graphenes of the present disclosure includepristine graphene. In some embodiments, the graphenes of the presentdisclosure include unfunctionalized graphene. In some embodiments, thegraphenes of the present disclosure include functionalized graphene thathas been functionalized with one or more functional groups. In someembodiments, the functional groups include, without limitation, oxygengroups, hydroxyl groups, esters, carboxyl groups, ketones, amine groups,nitrogen groups, and combinations thereof.

The graphenes of the present disclosure can have various carbon,nitrogen and oxygen contents. For instance, in some embodiments, thegraphenes of the present disclosure have a carbon content ranging fromabout 70 wt % to about 98 wt %. In some embodiments, the graphenes ofthe present disclosure have an oxygen content ranging from about 0 wt %to about 25 wt %. In some embodiments, the graphenes of the presentdisclosure have a nitrogen content ranging from about 0 wt % to about7.5 wt %.

Reaction Conditions

The methods of the present disclosure may occur under various reactionconditions. For instance, in some embodiments, the methods of thepresent disclosure can occur under ambient conditions. In someembodiments, the ambient conditions include, without limitation, roomtemperature, ambient pressure, and presence of air. In some embodiments,the methods of the present disclosure occur at room temperature in thepresence of air.

In some embodiments, the methods of the present disclosure can occur inthe presence of one or more gases. In some embodiments, the one or moregases include, without limitation, hydrogen, ammonia, argon nitrogen,oxygen, carbon dioxide, methane, ethane, ethene, chlorine, fluorine,acetylene, natural gas, and combinations thereof.

In some embodiments, the methods of the present disclosure can occur inan environment that includes ambient air. In some embodiments, theenvironment includes, without limitation, hydrogen, argon, methane, andcombinations thereof. Additional reaction conditions can also beenvisioned.

Graphene Materials

The methods of the present disclosure can be utilized to form varioustypes of graphene materials. In additional embodiments, the presentdisclosure pertains to the graphene materials that are formed by themethods of the present disclosure.

In some embodiments, the graphene materials of the present disclosureinclude a polymer and a graphene derived from the polymer. In someembodiments, the graphene is on a surface of the polymer. In someembodiments, the graphene materials of the present disclosure consistessentially of graphenes.

Suitable graphenes, polymers and polymer surfaces were describedpreviously. Suitable arrangements of graphenes on polymer surfaces werealso described previously (e.g., FIG. 1B). For instance, in someembodiments, the graphene includes a pattern on a surface of thepolymer. In some embodiments, the graphene is embedded with the polymer.In some embodiments, the graphene is on an outside surface of thepolymer. In some embodiments, the graphene is on a first surface of thepolymer. In some embodiments, the graphene is on a first surface and asecond surface of the polymer. In some embodiments, the first surfaceand the second surface are on opposite sides of the polymer.

Isolated Graphenes

The methods of the present disclosure can also be utilized to formvarious types of isolated graphenes. In additional embodiments, thepresent disclosure pertains to the isolated graphenes that are formed bythe methods of the present disclosure. In some embodiments, the isolatedgraphene is derived from a polymer and separated from the polymer.Suitable graphenes, polymers and polymer surfaces were describedpreviously.

Incorporation of Graphene Materials and Isolated Graphenes intoElectronic Devices

In some embodiments, the methods of the present disclosure also includea step of incorporating the graphene materials and isolated graphenes ofthe present disclosure into an electronic device. In some embodiments,the graphene materials and isolated graphenes of the present disclosureserve as a component of the electronic device. In additionalembodiments, the present disclosure pertains to methods of forming anelectronic device by forming a graphene material or an isolated grapheneof the present disclosure and incorporating the graphene material or theisolated graphene into the electronic device. In further embodiments,the present disclosure pertains to electronic devices that contain thegraphene materials or isolated graphenes of the present disclosure.

As set forth in more detail herein, the graphene materials and isolatedgraphenes of the present disclosure can be incorporated into variouselectronic devices in various manners. Furthermore, the graphenematerials and isolated graphenes of the present disclosure can serve asvarious electronic device components.

Electronic Device Formation

Various methods may be utilized to incorporate graphene materials andisolated graphenes into electronic devices. For instance, in someembodiments, the incorporation includes stacking a plurality of graphenematerials into the electronic device. In some embodiments, the graphenematerials are stacked in a series configuration. In some embodiments,the graphene materials are stacked in a parallel configuration.

The graphene materials and isolated graphenes of the present disclosurecan be incorporated into various electronic devices (e.g., FIGS. 1C-D).For instance, in some embodiments, the electronic device is an energystorage device or an energy generation device.

In some embodiments, the electronic device includes, without limitation,supercapacitors, micro supercapacitors, pseudo capacitors, batteries,micro batteries, lithium-ion batteries, sodium-ion batteries,magnesium-ion batteries, electrodes (e.g., conductive electrodes),sensors (e.g., gas, humidity and chemical sensors), photovoltaicdevices, electronic circuits, fuel cell devices, thermal managementdevices, biomedical devices, and combinations thereof. In someembodiments, the graphene materials and isolated graphenes of thepresent disclosure may be utilized in the electronic devices ascomponents of hydrogen evolution reaction catalysts, oxygen reductionreaction catalysts, oxygen evolution reaction catalysts, hydrogenoxidation reaction catalysts, and combinations thereof.

The incorporation of graphene materials and isolated graphenes of thepresent disclosure into electronic devices may result in the formationof various structures. For instance, in some embodiments, the electronicdevices of the present disclosure may be in the form of at least one ofvertically stacked electronic devices, in-plane electronic devices,symmetric electronic devices, asymmetric electronic devices, andcombinations thereof. In some embodiments, the electronic devices of thepresent disclosure include an in-plane electronic device. In someembodiments, the electronic devices of the present disclosure include aflexible electronic device.

In some embodiments, the electronic devices of the present disclosureinclude a super capacitor (SC), such as a flexible, solid-statesupercapacitor. In some embodiments, the electronic device is amicrosupercapacitor (MSC), such as a flexible microsupercapacitor or aflexible in-plane microsupercapacitor (MSC) (e.g., FIG. 1C). In someembodiments, the electronic devices of the present disclosure includevertically stacked electronic devices, such as vertically stackedsupercapacitors (e.g., FIG. 1D).

In some embodiments, the electronic devices of the present disclosuremay also be associated with an electrolyte. For instance, in someembodiments, the graphene materials and isolated graphenes of thepresent disclosure may be associated with an electrolyte. In someembodiments, the electrolyte may be placed between two graphenematerials in an electronic device. In some embodiments, the electrolyteincludes, without limitation, solid state electrolytes, liquidelectrolytes, aqueous electrolytes, organic salt electrolytes, ionliquid electrolytes, and combinations thereof. In some embodiments, theelectrolyte is a solid state electrolyte. In some embodiments, the solidstate electrolyte is made from inorganic compounds. In some embodiments,the solid state electrolyte includes polymeric electrolytes. In someembodiments, the solid-state electrolyte is made from poly(vinylalcohol) (PVA) and sulfuric acid (H₂SO₄).

Electronic Device Components

The graphenes associated with the graphene materials and isolatedgraphenes of the present disclosure can be utilized as variouselectronic device components. For instance, in some embodiments, thegraphenes of the present disclosure may be utilized as an electrode inan electronic device. In some embodiments, the graphenes of the presentdisclosure may be utilized as a positive electrode, a negativeelectrode, and combinations thereof. In some embodiments, the graphenesof the present disclosure may be utilized as interdigitated electrodes.

In some embodiments, the graphenes of the present disclosure may beutilized as conductive fillers in an electronic device. In someembodiments, the graphenes of the present disclosure may be utilized asconductive wires in an electronic device.

In some embodiments, the graphenes of the present disclosure may beutilized as a current collector in an electronic device. In someembodiments, the graphenes of the present disclosure may be utilized asa current collector and an electrode in an electronic device.

In some embodiments, the graphenes of the present disclosure may beutilized as additives in an electronic device. In some embodiments, theisolated graphenes of the present disclosure may be utilized asadditives in an electronic device, such as an energy storage device.

In some embodiments, the graphenes of the present disclosure are used inenergy storage devices. In some embodiments, the graphenes of thepresent disclosure are used as part of a battery anode. In someembodiments, the graphenes of the present disclosure are used as part ofa battery cathode. In some embodiments the graphenes of the presentdisclosure may be used in batteries as conductive fillers, such asanodes or as cathodes. In some embodiments, the graphenes of the presentdisclosure are utilized as additives in the electronic device.

Advantages

In some embodiments, the methods of the present disclosure provide aone-step and scalable approach for making various types of graphenematerials and isolated graphenes. In some embodiments, the methods ofthe present disclosure may employ roll-to-roll manufacturing processesfor more efficient manufacturing of the graphene materials and isolatedgraphenes. In some embodiments, the methods of the present disclosuremay be utilized to form graphene materials and isolated grapheneswithout the utilization of any metals, such as metal surfaces or metalcatalysts.

The graphenes of the graphene materials and isolated graphenes of thepresent disclosure can have various advantageous properties. Forinstance, in some embodiments, the electrochemical performance of thegraphenes is enhanced with three times larger areal capacitance and 5 to10 times larger volumetric energy density at various power densities. Insome embodiments, the graphenes have decomposition temperatures of morethan about 900° C. In some embodiments, the graphenes are stable attemperatures up to about 2,000° C. In some embodiments, the graphene hashigh electrical conductivity.

As such, electronic devices that contain the graphene materials andisolated graphenes of the present disclosure can have variousadvantageous properties. For instance, in some embodiments, theelectronic devices of the present disclosure have a capacitance rangingfrom about 2 mF/cm² to about 1000 mF/cm². In some embodiments, theelectronic devices of the present disclosure have a capacitance rangingfrom about 10 mF/cm² to about 20 mF/cm². In some embodiments, theelectronic devices of the present disclosure have a capacitance of morethan about 4 mF/cm². In some embodiments, the electronic devices of thepresent disclosure have a capacitance of more than about 9 mF/cm². Insome embodiments, the electronic devices of the present disclosure havea capacitance of about 16.5 mF/cm².

In some embodiments, the electronic devices of the present disclosureretain at least 90% of their capacitance value after more than 10,000cycles. For instance, in some embodiments, the electronic devices of thepresent disclosure retain at least 95% of their capacitance value aftermore than 10,000 cycles. In some embodiments, the electronic devices ofthe present disclosure retain at least 90% of their capacitance valueafter more than 7,000 cycles. In some embodiments, the electronicdevices of the present disclosure retain at least 90% of theircapacitance value after more than 9,000 cycles.

In some embodiments, the capacitance of the electronic devices of thepresent disclosure increase by at least 110% of their original valueafter more than 10,000 cycles. For instance, in some embodiments, thecapacitance of the electronic devices of the present disclosure increaseby at least 110% of their original value after more than 2,500 cycles.

In some embodiments, the electronic devices of the present disclosurehave power densities that range from about 5 mW/cm² to about 200 mW/cm².In some embodiments, the electronic devices of the present disclosurehave power densities of about 9 mW/cm².

Reference will now be made to more specific embodiments of the presentdisclosure and experimental results that provide support for suchembodiments. However, Applicants note that the disclosure below is forillustrative purposes only and is not intended to limit the scope of theclaimed subject matter in any way.

Example 1. Laser-Induced Porous Graphene Films from Commercial Polymers

In this Example, a one-step, scalable approach for producing andpatterning porous graphene films with 3-dimensional (3D) networks fromcommercial polymer films using a CO₂ infrared laser is reported. Thesp³-carbon atoms are photothermally converted to sp²-carbon atoms bypulsed laser irradiation. The resulting laser-induced graphene (LIG)exhibits high electrical conductivity. Moreover, the LIGs can be readilypatterned to interdigitated electrodes for in-plane microsupercapacitorswith specific capacitances of >4 mF·cm⁻² and power densities of ˜9mW·cm⁻². As such, the materials demonstrate a new application in energystorage.

It has recently been demonstrated that fabrication of MSCs usingconventional lithography techniques requires masks and restrictedoperational conditions. While there have been recent developments inlaser-scribing hydrated graphene oxide (GO) films, Applicants show inthis Example a one-step laser-scribing method on commercial polymerfilms in air to form 3D graphene layers. The approach is scalable andcost-effective in fabricating large-area devices. Moreover, the approachcan be transferrable to a roll to roll process.

Example 1.1. Laser Scribing

As depicted in FIGS. 2A and 3A, irradiation of a commercial polyimide(PI) film by a CO₂ infrared laser under ambient conditions converts thefilm into porous graphene (also referred to as laser-induced graphene(LIG)). With computer-controlled laser scribing, LIG can be readilywritten into various geometries, as shown in the scanning electronmicroscopy (SEM) image in FIGS. 2B, 3B and 3C. The photographs in FIGS.3B-C show two distinguished areas: black LIG after PI was exposed to thelaser, and light orange PI that was unexposed.

Without being bound by theory, theoretical calculations partiallysuggest that enhanced capacitance may result from LIG's unusualultra-polycrystalline lattice of pentagon-heptagon structures. Combinedwith the advantage of one-step processing of LIG in air from commercialpolymer sheets, which would allow the employment of a roll-to-rollmanufacturing process, this technique provides a rapid route topolymer-written electronic and energy storage devices.

Example 1.2. Analytical Characterization

LIG films obtained with a laser power of 3.6 W, denoted as LIG-3.6 W,were further characterized with SEM, Raman spectroscopy, X-raydiffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fouriertransform infrared (FTIR) spectroscopy. FIG. 2C shows that LIG filmsexhibit the appearance of a foam with porous structures resulting fromthe rapid liberation of gaseous products. Cross-sectional SEM images ofLIG reveal ordered porous morphology (FIG. 2D). These porous structuresrender enhanced accessible surface areas and facilitate electrolytepenetration into the active materials.

The Raman spectrum of LIG (FIG. 2E) shows three prominent peaks: the Dpeak at ˜1350 cm⁻¹ induced by defects or bent sp²-carbon bonds, thefirst-order allowed G peak at ˜1580 cm⁻¹, and the 2D peak at ˜2700 cm⁻¹originating from second order zone boundary phonons. If PI is carbonizedat temperatures ranging from 800 to 1500° C., the resulting Ramanspectrum is similar to that of glassy carbon (FIG. 4). However, thespectrum for LIG (FIG. 2E) is clearly different from that of glassycarbon. The 2D peak of LIG can be fitted with only one Lorentzian peakcentered at 2700 cm⁻¹, the same as in single-layer graphene (SLG), butwith a larger full width at half maximum (FWHM) of ˜60 cm⁻¹. This 2Dband profile is typical of that found in 2D graphite consisting ofrandomly stacked graphene layers along the c axis. Finally, D/Gintensity ratio indicates a high degree of graphene formation in the LIGfilms.

The XRD pattern (FIG. 2F) shows an intense peak centered at 2θ=25.90,giving an interlayer spacing (I_(c)) of ˜3.4 Å between (002) planes inthe LIG. The pattern indicates the high degree of graphene formation.The asymmetry of the (002) peak, with tailing at smaller 2θ angles, alsopoints to an increased I_(c). The expanded I_(c) can be attributed toregions where defects are distributed on hexagonal graphene layers. Thepeak at 2θ=42.90 is indexed to (100) reflections which are associatedwith an in-plane structure. Using equations 2 and 3, and the methodsdescribed in this Example, the crystalline size along the c-axis (L_(c))and a-axis (L_(a)) are calculated to be ˜17 nm and ˜32 nm, respectively.

The XPS spectrum of LIG-3.6 W shows a dominant C—C peak with greatlysuppressed C—N, C—O and C═O peaks (FIG. 5). Such results suggest thatLIG films are dominated by sp²-carbons, agreeing well with the Raman andXRD results. This is further confirmed by comparison of the distinctiveFTIR spectra of PI and LIG-3.6 W (FIG. 6).

The micro- and nano-structure of LIG flakes was investigated bytransmission electron microscopy (TEM). FIG. 7A shows thin LIG flakeswith few-layer features as further indicated from the edges of the flakein FIG. 8A. Moreover, ripple-like wrinkled structures can be observedfrom the surface of the flakes. These structures in graphene have beenshown to improve the electrochemical performance of devices. Thickerflakes exhibit mesoporous structures (FIG. 7B). High-resolution TEM(HRTEM) images in FIG. 8B reveals that the nano-shaped ripples areexposed edges of graphene layers. The formation of these ripples couldbe attributed to thermal expansion caused by laser irradiation. Theaverage lattice space of ˜3.4 Å shown in FIG. 8B corresponds to thedistance between two neighboring (002) planes in graphitic materials,and it agrees well with the XRD results. The aberration-correctedscanning transmission electron microscopy (Cs-STEM) image (FIG. 8C)shows the unusual ultra-polycrystalline feature of LIG flakes withdisordered grain boundaries. This observation is further depicted inFIG. 8D, where a hexagon lattice and a heptagon with two pentagons isshown. These abundant pentagon-heptagon pairs can account for thecurvature of the graphene layers leading to the porous structure (FIGS.7C-D and 9). Theoretical calculations suggest that the aforementioneddefects could enhance electrochemical capacity (as discussed in detailherein).

LIG has a surface area of ˜340 m²·g⁻¹ by BET, with pore sizes of lessthan 9 nm (FIG. 10). Thermogravimetric analysis (TGA) measurement underargon (FIG. 11) shows that the decomposition temperature of PI is ˜550°C. and LIG is >900° C., while that of the often used graphene precursor,graphene oxide (GO), is ˜190° C.

Example 1.3. Effect of Laser Power

To investigate the effect of laser power, LIG was prepared using powersranging from 2.4 W to 5.4 W in 0.6 W increments at a scan rate of 3.5inches per second. In FIG. 12A (plotted from Table 1), beginning at 2.4W, the atomic percentage of carbon sharply increases from the original71% in PI to 97% in LIG while the atomic percentages of both nitrogenand oxygen decrease precipitously to <3%. This threshold power effecthas been well-studied in UV ablation of polymers.

Materials Carbon (%) Oxygen (%) Nitrogen (%) Polyimide 70.5 22.5 7.0LIG-1.2 W 72.2 20.3 7.5 LIG-1.8 W 74.7 18.2 7.1 LIG-2.4 W 97.3 2.5 0.2LIG-3.0 W 95.5 4.1 0.4 LIG-3.6 W 94.5 4.9 0.6 LIG-4.2 W 94.0 5.5 0.5LIG-4.8 W 92.3 6.9 0.8 LIG-5.4 W 91.3 7.7 1.0Table 1 provides a summary of atomic percentage of elements in rawmaterial (PI) and LIG derived from different laser powers. All of thedata were obtained by high-resolution XPS scans.

The threshold power shows a linear dependence on the scan rate (FIG.13). If the scan rate increases, higher threshold power needs to beapplied in order to initiate the graphitization. Meanwhile, the sheetresistance (R_(s)) of LIG-2.4 W is reduced to <35 Ω □⁻¹ (FIG. 12B).Below the threshold of 2.4 W, PI is an insulator with R_(s)>>90 MΩ □⁻¹(instrument limit). As the laser power increases to 5.4 W, R_(s) isgradually reduced to a minimum value of <15 Ω □⁻¹; the translatedconductivity is ˜25 S·cm⁻¹, higher than in laser-reduced GO. FIG. 12Bshows two distinct slopes of Rs vs. laser power. The slope when thelaser power was <4.2 W is larger than the one when it was >4.2 W. Thissuggests that when the laser power is <4.2 W, the thermal powerdominates the quality of the films. Therefore, increased laser powerleads to higher graphene formation. As the thermal power rises above 4.2W, oxidation starts to play an increasingly deleterious role in thequality of the films. Therefore the slope lessens.

As expected, higher laser power tends to increase porosity, as shown inthe SEM images taken on the backsides of the LIG films (FIG. 14) thathad been peeled off the PI substrate. Raman spectroscopy is a powerfultool to obtain crystalline size (L_(a)) along the a-axis of graphiticmaterials by analyzing ratios of the integrated intensities of G and Dpeaks (I_(G)/I_(D)). FIG. 12C shows representative Raman spectra of LIGfilms attained with laser powers from 2.4 to 5.4 W. The statisticalanalysis of I_(G)/I_(D) vs. laser powers is plotted in the upper panelof FIG. 12D. The L_(a) values calculated from the average I_(G)/I_(D)ratio using eq 4 and the methods described in this Example is shown inthe lower panel of FIG. 12D, showing increased L_(a) up to ˜40 nm as thelaser power rises to 4.8 W. This increase can be attributed to increasedsurface temperatures. Further increase in power degrades the quality ofthe LIG with L_(a) of ˜17 nm in LIG-5.4 W, which is attributable to thepartial oxidation of LIG in air. This can be further verified fromprofound defect-correlated D′ peaks centered at ˜1620 cm⁻¹ in LIG-5.4 W(FIG. 12C).

Example 1.4. Discussion

Laser ablation of polymers has been studied since the early 1980s.Because of its complex nature, the detailed mechanism is still debatedas being a photothermal or photochemical process, or both. Sincephotochemical processes tends to occur in lasers with short wavelengthsand ultra-short pulse widths, Applicants' infrared LIG formation is morelikely to be caused by photothermal effects due to its long wavelength(˜10.6 μm) and relatively long pulses (˜14 μs). The energy from laserirradiation results in lattice vibrations which could lead to extremelyhigh localized temperatures (>2500° C.) that can be qualitativelydetected by laser-induced fluorescence. This high temperature couldeasily break the C—O, C═O and N—C bonds, as confirmed by thedramatically decreased oxygen and nitrogen contents in LIG (FIG. 12A).These atoms would be recombined and released as gases. Aromaticcompounds are then rearranged to form graphitic structures, during whichoxidation of these graphitic structures can be minimized by an overlayerof the evolved gases.

Without being bound by theory, Applicants have found that the mechanismof laser graphitization in polymers is strongly correlated to thestructural features present in the repeat units, such as aromatic andimide repeat units. Attempts were made to generalize this laser inducedgraphitization process by testing 15 different polymers. Out of them,only two polymers, PI and poly(etherimide) (PEI), both of which containaromatic and imide repeat units, can form LIG in this example (Table 2and FIG. 15). Four other step growth polymers and all 9 of the chaingrowth polymers tested did not afford LIG in this Example. The reasonfor other step growth polymers being inactive is not conclusively known,but suggested by the fact that at 10.6 μm, the CO₂ laser wavelength hasa strong absorbance in the polyimide film (FIG. 59). However, use oflasers that have other wavelengths can be used to target polymers thathave absorbances at the laser wavelength line. Additionally, one couldadd a compound to a polymer wherein the added compound absorbs well atthe frequency of the laser used, and that additive becomesspectroscopically excited by the laser, thereby transferring its energy,thermally or photochemically, to the polymer, causing the polymer toform graphene. In some cases the added compound would act as asensitizer.

Full Name Symbols Unit Graphitized? Kapton Polyimide PI

Yes Ulse Polyetherimide PEI

Yes Polyether ether ketone PEEK

No Polyethylene terephthalate PET

No Polyethylene naphthalate PEN

No Fluorinated ethylene propylene FEP

No Perfluoroalkoxy alkanes PFA

No Teflon PTFE

No Polystyrene PS

No Polycarbonate PC

No Polyethylene PE

No Polyvinyl alcohol PVA

No Poly(methyl methacrylate) PMMA

No Acrylonitrile butadiene styrene ABS

No Poly(acrylonitrile) PAN

NoTable 2 provides a summary of polymers, their chemical repeat units andtheir LIG-forming capability. Out of 15 polymers, only PI and PEI weresuccessfully converted to LIG in this example. Nonaromatic hydrocarbonsundergo almost complete degradation without graphene formation.Formation of LIG from poly- or heterocyclic structures such as the imidegroup in PI and PEI polymers favor LIG formation. PAN films are notcommercially available and were thus prepared in-house. Though PAN is aprecursor to carbon fiber, it does not form graphene well unless heatedslowly to permit cyclization and N-extrusion.

Example 1.5. Fabrication of LIG-MSCs

Next, Applicants fabricated in-plane interdigitated LIGmicrosupercapacitors (LIG-MSCs) in which LIG serves as both the activeelectrodes and the current collectors. Well-defined LIG-MSC electrodesare directly written on PI sheets with a neighboring distance of ˜300 μm(FIGS. 16A-B). This distance can be further decreased by using a smallerlaser aperture. After writing, silver paint was applied on commonpositive and negative electrodes, and then Kapton tape was employed todefine the active electrodes.

FIG. 16C depicts the device architecture of the fabricated LIG-MSCs.Cyclic voltammetry (CV) and galvanostatic charge-discharge (CC)measurements were performed to investigate the electrochemicalperformance of the fabricated LIG-MSCs. All CV curves of LIG-MSCs madewith LIG electrodes at various laser powers are pseudo-rectangular inshape, which indicates good double-layer capacitive behaviors (FIG. 17).LIG-MSCs constructed with LIG-4.8 W electrodes generally exhibit thehighest specific areal capacitance (C_(A)) (FIG. 17B). The C_(A) ofLIG-MSCs made from PEI is ˜10% of those from PI (FIGS. 17C-D), possiblyassociated with the lower nitrogen content. Therefore, all otherelectrochemical measurements were carried out on LIG-MSCs made from PIwith a laser power of 4.8 W. FIGS. 16D-E are the CV curves at scan ratesranging from 20 to 10,000 mV·s⁻¹. Although there exist certain levels ofoxygen or nitrogen contents in LIG, the devices do not exhibitpseudo-capacitive behavior, as suggested from CV curves at a small rateof 20 mV·s⁻¹, which shows no anodic and cathodic peaks. Even at a highrate of 10,000 mV·s⁻¹, the CV curve maintains its pseudo-rectangularshape, and this is suggestive of high power performance. The C_(A) as afunction of scan rate is shown in FIG. 16F. At a scan rate of 20 mV·s⁻¹,the C_(A) is >4 mF·cm⁻², which is comparable to or higher than thevalues obtained in recently reported GO-derived supercapacitors. Thespecific capacitance of the material by weight is ˜120 F·g⁻¹. At 10,000mV·s⁻¹, the C_(A) is still higher than 1 mF·cm⁻². This optimalcapacitive behavior is further confirmed by the nearly triangular CCcurves at varying current densities from 0.2 to 25 mA·cm⁻² (FIGS.16G-H). From the C_(A) vs. discharge current densities (I_(D)) plottedin FIG. 16I, the LIG-MSCs can deliver C_(A) of ˜3.9 mF·cm⁻² at I_(D) of0.2 mA·cm⁻² and still maintain 1.3 mF·cm⁻², even when the devices areoperated at I_(D) of 25 mA·cm⁻². This value is comparable or higher thanthose reported for some carbon-based MSCs at the same current densities.The impedance measurement shows a low equivalent series resistance of 7Ω(FIG. 18).

Other than aqueous electrolyte, Applicants also explored the use of anionic liquid electrolyte in LIG-MSCs. FIG. 19 shows CV and CC curves ofLIG-MSCs in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF₄),which suggest optimal capacitive behaviors. The corresponding specificvolumetric capacitances (C_(V)) vs. discharge volumetric currentdensities (I_(D)) is shown in FIG. 20.

For practical applications requiring either higher operation potentialor current or both, supercapacitors need to be connected in serialand/or parallel configurations. As shown in FIG. 21, the outputpotentials and currents can be well-controlled by serial and parallelconnections to power light-emitting diodes (LEDs). Compared withcommercial devices such as aluminum electrolytic capacitors (AECs), thinfilm Li-ion batteries, and activated carbon supercapacitors (AC-SCs),LIG-MSCs offer more energy or power density or both as seen from theRagone plots (FIG. 22). When compared with recently demonstrated reducedGO-film (called MPG films) MSCs (MPG-MSCs) and laser-scribed grapheneMSCs (LSG-MSCs), LIG-MSCs can deliver comparable E_(V), although powerperformance needs to be enhanced. Using specific areal energies (E_(A))and power (P_(A)) densities, one can obtain reasonable values forcomparing performance of in-plane MSCs intended for commercialapplications. FIG. 22B shows that LIG-MSCs exhibit ˜100× higher E_(A)and ˜4×P_(A) than MPG-MSCs. Furthermore, LIG-MSCs offer slightly betterE_(A) than LSG-MSCs with comparable power performance. In addition,cycling performance shows that there is negligible capacitance degradingafter 9000 cycles in aqueous electrolytes and 7000 cycles in ionicliquid electrolytes (FIG. 23). Moreover, CV curves at every 1000 cyclesshow no involved pseudo-capacitive peaks (FIG. 24).

Without being bound by theory, it is envisioned that the highcapacitance of the LIG-MSC can be attributed to the 3D network of highlyconductive graphene showing high surface area and abundant wrinkles,which provide easy access for the electrolyte to form a Helmholtz layer.Moreover, density function theory (DFT) calculations suggest that theultra-polycrystalline nature of LIG-MSC can also improve thecapacitance. The total capacitance (C) is contributed by the quantumcapacitance (C_(q)), and the liquid electrolyte (C₁) consisting ofHelmholtz and diffusion regions: C⁻¹=C_(q) ⁻¹+C₁ ⁻¹. C₁ is mostlycontrolled by surface area. C_(q) represents the intrinsic property ofthe electrode material and can be calculated from its electronicstructure in eq 1:

$\begin{matrix}{{C_{q}(V)} = {\frac{1}{SV}{\int_{0}^{V}{{{eD}\left( {ɛ_{F} - {e\; V^{\prime}}} \right)}\ {dV}^{\prime}}}}} & (1)\end{matrix}$

In equation 1, S is the surface area, V is the applied voltage, D is thedensity of states, ε_(F) is the Fermi level, and e is the electroncharge. The ultra-polycrystalline nature suggested by FIGS. 8C-D as wellas FIG. 12D indicate the abundance of grain boundaries (GBs), which arecomposed of pentagon and heptagon pairs. These defects are more‘metallic’ than regular hexagons, and therefore can be expected toenhance the charge storage performance. Calculations are performed byusing DFT. The GB effect is modeled by a planar polycrystalline graphenesheet (FIG. 25). Two types of GBs are considered as representatives(FIGS. 16J-K).

As another case, Applicants also consider a graphene sheet fullycomposed of pentagons and heptagons (FIG. 16L, also referred to as a“pentaheptite.”). The calculated C_(q) is shown in FIG. 16N. Clearly, apolycrystalline sheet has a much higher C_(q) than perfect graphene, asa result of a higher density of states near the Fermi level due to thepresence of GBs. The type II GB enhances the storage more than in typeI, as it has a higher defect density along the GBs. The highest C_(q) isfound in pentaheptite due to its highest disorders and metallicity.Though here only the C_(q) is calculated, it can be expected that theC_(tot) increases as C_(q) increases. These results suggest thatGBs-rich LIG with maintained electric conductivity would be able todeliver higher capacitance than perfect defect-free graphitic materials.Chemical doping of its rich ultra-polycrystalline domains ofpentagon-heptagon rings might further enhance the capacitance. This isthe first theoretical calculation that shows the effect ofpentagon-heptagon grain boundaries on charge storage, a result thatcould inspire theoreticians to further explore the potential of thesematerials.

In summary, Applicants have demonstrated in this Example a one-step andscalable approach for the preparation of porous graphene from commercialpolymer sheets using CO₂ laser irradiation under ambient conditions.Applicants have established that the physical and chemical properties ofthe resulting LIG structures render them uniquely suitable for energystorage devices delivering promising electrochemical performance. Theuse of commercially available polymer sheets would allow forroll-to-roll manufacturing, which can facilitate commercialization.Theoretical modeling suggests that the enhanced capacitance couldpartially come from defect-rich boundaries in LIG.

Example 1.7. Methods

Kapton polyimide (PI, Cat. No. 2271K3, thickness: 0.005″) and otherpolymers sheets used in this Example were all purchased fromMcMaster-Carr unless stated otherwise. The polymers were used asreceived unless noted otherwise. Laser scribing on polymer sheets wereconducted with a carbon dioxide (CO₂) laser cutter system (UniversalX-660 laser cutter platform): 10.6 μm wavelength of laser with pulseduration of ˜14 μs. The beam size is ˜120 μm. Laser power was variedfrom 2.4 W to 5.4 W with increments of 0.6 W. The laser system offers anoption of controlling the scan rates from 0.7 to 23.1 inches per second.The laser system also provides an option of setting pulses per inch(ppi) with a range from 10 to 1000 ppi. By experimentation it wasdiscovered that the ppi rate played little role in changing thethreshold power. Other than as specifically stated, the same scan rateof 3.5 inch/s and 1000 ppi were used for all experiments. All of thelaser experiments were performed under ambient conditions.

Example 1.8. Device Fabrication

LIG electrodes were directly written using the computer-controlled CO₂laser. In the MSCs, the LIG serves as both the active electrodes andcurrent collectors. For better electrical connection, silver paint wasapplied on the common areas of the positive and negative electrodes. Theelectrodes were extended with conductive copper tapes and then connectedto electrochemical workstation. To protect the contact pads from theelectrolyte, Kapton polyimide tape was employed to define theinterdigitated area (FIG. 16C).

Example 1.9. Characterization

SEM images were taken on a FEI Quanta 400 high resolution field emissioninstrument. The TEM and HRTEM were performed using a 2100F fieldemission gun. Aberration-corrected scanning transmission electronmicroscopy (Cs-STEM) images were taken using an 80 KeV JEOL ARM200Fequipped with a spherical aberration corrector. The LIG films werepeeled off and sonicated in chloroform before being transferred onto aC-flat TEM grid. X-ray photoelectron spectroscopy (XPS) was performedusing a PHI Quantera SXM Scanning X-ray Microprobe with a base pressureof 5×10⁻⁹ Torr. All of the survey spectra were recorded in 0.5 eV stepsize with a pass energy of 140 eV. Elemental spectra were recorded in0.1 eV step sizes with a pass energy of 26 eV. All the spectra werecorrected using C1s peaks (284.5 eV) as references. X-ray diffraction(XRD) was conducted on a Rigaku D/Max ultima II with Cu Kα radiation(λ=1.54 Å). A Renishaw Raman microscope using 514-nm laser excitation atroom temperature with a laser power of 5 mW was employed to obtain Ramanspectra. A Nicolet infrared spectroscope was used to acquire the FTIRspectra. The surface area of LIG was measured with a Quantachromeautosorb-3b BET surface analyzer. TGA (Q50, TA Instruments) thermogramswere carried out between 100° C. to 900° C. at 5° C.·min⁻¹ under argon;the water content was calculated from the weight loss between roomtemperature and 100° C. The sheet resistances were measured using aKeithley four-point probe meter (model: 195A, detection limit: 20 MΩ).The LIG samples for XRD, BET and TGA experiments were powder scratchedfrom LIG films. Other characterizations were conducted directly on LIGfilms.

The crystalline size (L_(c)) along the c-axis and domain size in thea-axis (L_(a)) and of LIG are calculated from the characteristics of theXRD (002) and (100) peaks using the eqs 2 and 3, respectively:

$\begin{matrix}{L_{c} = \frac{0.89\lambda}{{B_{1/2}\left( {2\;\theta} \right)}\cos\;\theta}} & \left( {{eq}\mspace{14mu} 2} \right) \\{L_{a} = \frac{1.84\lambda}{{B_{1/2}\left( {2\;\theta} \right)}\cos\;\theta}} & \left( {{eq}\mspace{14mu} 3} \right)\end{matrix}$

In the above equations, λ is the wavelength of the X-ray (λ=1.54 Å) andB_(1/2) (2θ) (in radian units) is the full width at half-maximum of thepeaks (200) and (100). Using Raman spectroscopic data, and calculatingthe crystalline size in the a-axis (L_(a)) from the ratio of integratedintensity of the G peak (I_(G)) and D peak (I_(D)), the L_(a) can beobtained by eq 4:

$\begin{matrix}{L_{a} = {\left( {2.4 \times 10^{- 10}} \right) \times \lambda_{l}^{4} \times \left( \frac{I_{G}}{I_{D}} \right)}} & \left( {{eq}\mspace{14mu} 4} \right)\end{matrix}$

In the above equation, λ_(l) is wavelength of the Raman laser (λ_(l)=514nm).

Example 1.10. Measurements

CV, galvanostatic CC measurements, and electrochemical impedancespectroscopy (EIS) were performed using a CHI 608D workstation (USA).All of measurements were conducted in ambient conditions for aqueouselectrolytes (1 M H₂SO₄). The LIG-MSCs using 1-butyl-3-methylimidazoliumtetrafluoroborate (BMIM-BF₄, Sigma-Aldrich) were assembled and measuredin an argon-filled glove box (VAC, model: NEXUS) with controlled O₂ andH₂O levels lower than 1 ppm. To ensure full diffusion of ions ontosurfaces of LIG electrodes, the microdevices were soaked in electrolytefor 2 to 3 h before measurements. EIS was performed using the sinusoidalsignal of 10 mV amplitude at a frequency ranging from 10 mHz to 100 kHz.

Example 1.11. Calculation of Parameters as Indications forElectrochemical Performance of LIG-MSCs

The specific areal capacitances (C_(A), in mF·cm⁻²) based on the CVcurves were calculated by eq 5:

$\begin{matrix}{C_{A} = {\frac{1}{2 \times S \times v \times \left( {V_{f} - V_{i}} \right)}{\int_{V_{i}}^{V_{f}}{{I(V)}\ {dV}}}}} & \left( {{eq}\mspace{14mu} 5} \right)\end{matrix}$

In the above equation, S is the total surface area of active electrodes(in cm²) with 0.6 cm² for the devices configuration used in this work; vis the voltage sweep rate (in V·s⁻¹); V_(f) and V_(i) are the potentiallimits of CV curves; and I(V) is the voltammetric current (in amperes).∫_(V) _(i) ^(V) ^(f) I(V)dV is the integrated area from CV curves.

The total surface area of the device including the spacing betweenelectrodes was ˜0.86 cm², which is used for calculating the power andenergy density in the Ragone plot shown in FIG. 22. The specific areal(C_(A), in mF·cm⁻²) and volumetric capacitance (C_(V), in F·m³) werecalculated from charge-discharge (CC) curves by eq 6 and 7:

$\begin{matrix}{C_{A} = \frac{I}{S \times \left( {{dV}/{dt}} \right)}} & \left( {{eq}\mspace{14mu} 6} \right) \\{C_{V} = \frac{C_{A}}{d}} & \left( {{eq}\mspace{14mu} 7} \right)\end{matrix}$

In the above equations, I is the discharge current (in amperes) anddV/dt is the slope of galvanostatic discharge curves. S is the totalarea of the active positive and negative electrodes and d is thethickness of active materials. For the devices used in FIGS. 18 and 20A,d was ˜25 μm.

The specific areal (E_(A), in μWh·cm⁻²) and volumetric energy densities(E_(V), in Wh·m⁻³) were calculated from eq 8 and 9:

$\begin{matrix}{E_{A} = {\frac{1}{2} \times C_{A} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & \left( {{eq}\mspace{14mu} 8} \right) \\{E_{V} = {\frac{1}{2} \times C_{V} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & \left( {{eq}\mspace{14mu} 9} \right)\end{matrix}$

In the above equations, ΔV=V_(max)−V_(drop) is the discharge potentialrange (V_(max) is the maximum voltage, 1 V for H₂SO₄, 3.5 V forBMIM-BF₄), V_(drop) is voltage drop indicated from the difference of thefirst two data points in the discharge curves. The specific areal(P_(A), in mW·cm²) and volumetric (P_(V), in W·cm³) power densities wereobtained from eq 10 and 11:

$\begin{matrix}{P_{A} = {\frac{E_{A}}{\Delta\; t} \times 3600}} & \left( {{eq}\mspace{14mu} 10} \right) \\{P_{V} = {\frac{E_{V}}{\Delta\; t} \times 3600}} & \left( {{eq}\mspace{14mu} 11} \right)\end{matrix}$

In the above equations, Δt is discharge time (in s).

Example 1.12. DFT Calculations of Perfect and Polycrystalline GrapheneLayers

DFT calculations were performed with projector-augmented wavepseudopotentials and Perdew-Burke-Ernzerhof exchange-correlationfunctional, as implemented in VASP. All structures were relaxed untilthe force on each atom was <0.01 eVÅ⁻¹. Two types of polycrystallinesheets are considered, as shown in FIG. 21. Monkhorst-Pack (MP) k-pointssampling is used, with a vacuum space >15 Å in the non-periodicdirection. To obtain the density of states (DOS), Applicants used thetetrahedron method with Blöchl corrections with a 45×7×1 k-points mesh.

Example 2. Fabrication of Flexible Boron-Doped Laser Induced GrapheneMicrosupercapacitors

In this Example, Applicants demonstrate that boron-doped porous graphenecan be prepared in ambient air using a facile laser induction processfrom boric acid containing polyimide sheets. At the same time, activeelectrodes can be patterned for flexible microsupercapacitors. As aresult of boron doping, the highest areal capacitance of as-prepareddevices reaches 16.5 mF/cm², three times higher than non-doped devices,with concomitant energy density increases of 5 to 10 times at variouspower densities. The superb cyclability and mechanical flexibility ofthe device is also well-maintained.

In particular, Applicants report in this Example that boron-doped LIG(B-LIG) can be synthesized with a laser induction method that isperformed in air using a standard commercial laser writing tool as foundin common machine shops. The synthesis starts by dissolving H₃BO₃ intopoly(pyromellitic dianhydride-co-4,4′-oxydianiline amic acid) (orpoly(amic acid), PAA) solution as a boron precursor, followed bycondensation of the PAA to produce boric acid containing PI sheet.Subsequent laser induction using a commercial CO₂ laser writes patternson the as-prepared PI sheet under ambient conditions. During the laserinduction, the surface of the PI sheet, with its H₃BO₃, transforms intoB-LIG. At the same time, the B-LIG on the PI film can be patterned intointerdigitated shapes for flexible MSCs.

The resulting B-LIG has significantly improved electrochemicalperformance over the non-doped structures, with three times highercapacitance and 5 to 10 times higher energy density than Applicantsachieved in pristine boron-free samples (e.g., Example 1). Thetransformation of PAA to PI is preferred for the successful formation ofLIG with high electrochemical properties. Meanwhile, the cyclability andflexibility of as-prepared devices are well-maintained, demonstratingthe potential of B-LIG materials for future low-cost energy storagedevices.

FIG. 26A shows a scheme for the synthesis and patterning process ofB-LIG materials for MSCs. Starting with a 12.8 wt % PAA solution in NMP,various weight percentages of H₃BO₃ (0, 1, 2, 5 and 8 wt % relative toPAA) were added and mixed under bath-sonication for 30 minutes to form auniform precursor solution. Next, the solution was poured into analuminum dish and the solvent removed in a vacuum oven at 60° C. for 3days, resulting in a solid PAA/H₃BO₃ sheet. The PAA/H₃BO₃ sheet was thenplaced in a hydraulic press (Carver press) and heated to 200° C. for 30min under a pressure of ˜0.3 MPa to dehydrate the PAA/H₃BO₃ sheet andform the PI/H₃BO₃ film. During this step, PAA and H₃BO₃ will dehydrateand transform into PI and BO_(x) as shown in FIG. 26B. The dehydrationfrom PAA to PI is preferred for successful formation of LIG and will bediscussed in detail herein.

Finally, a standard CO₂ laser cutting system was used under ambientconditions to convert PI/H₃BO₃ to xB-LIG (x=0, 1, 2, 5, and 8, whichdenotes the initial H₃BO₃ loading weight percentages). Optical images ofthe PAA/H₃BO₃ solution and patterned B-LIG on a PI/H₃BO₃ sheet arepresented in FIG. 27.

Here, the incorporation of H₃BO₃ into the PAA was preferable. Attemptsto incorporate boron from sources other than H₃BO₃, including ammoniaborane and m-carborane, resulted in little or no boron doping of theLIG. Without being bound by theory, Applicants envision that this isbecause boric acid dehydrates and polymerizes on heating while the othertwo evaporate or sublime, causing the failure of boron doping. The majoradvantage of this synthetic process is that B-LIG can be fabricated andpatterned at the same time during laser induction, making it an idealmaterial for future roll-to-roll processing.

The morphology of formed B-LIG was characterized using scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM). FIG. 26Cshows an SEM image of the as-prepared 5B-LIG that exhibits a porousstructure due to the rapid formation of gaseous products during laserinduction. The inset in FIG. 26C reveals that the thickness of 5B-LIG onthe PI sheet surface is ˜25 μm. FIG. 26D shows the TEM image of 5B-LIGat low magnification containing few-layer graphene structures withnanoscale ridges and wrinkles, which would be beneficial for higheraccessible surface area and therefore enhanced electrochemicalperformance.

High-resolution TEM (HRTEM) image in FIG. 26E further confirms thegraphitic nature of the 5B-LIG nanosheet. Numerous graphene edges werefound on the surface of the 5B-LIG nanosheet, again indicating a highlyaccessible surface area. For comparison, LIG materials with differentloadings of H₃BO₃ (0B-LIG, 1B-LIG, 2B-LIG, and 8B-LIG) were alsoprepared and imaged with SEM and TEM (FIGS. 28-29). No significantdifference was found among these samples, indicating that the loading ofH₃BO₃ has little effect on the morphology of the resulting LIG.

Raman spectroscopy and powder X-ray diffraction were further used tocharacterize the morphology of the B-LIG material. The Raman spectrum of5B-LIG in FIG. 30A shows three characteristic peaks for graphene derivedmaterial: the D peak at ˜1350 cm⁻¹ induced by defects or disordered bentsites, the G peak at ˜1590 cm⁻¹ showing graphitic sp² carbon, and the 2Dpeak at ˜2700 cm⁻¹ originating from second order zone boundary phonons.The large D peak observed here could arise from numerous graphene edges,consistent with TEM observations (FIG. 26E), boron doping into the LIGsheets, or the bending of the graphene layers in the porous structure.

The XRD pattern in FIG. 30B shows a prominent peak at 2θ=260, indicatingan interlayer spacing of ˜3.4 Å between (002) graphitic crystal planesin 5B-LIG. A (100) graphitic crystal phase was also found at 2θ=430. Thehigh degree of graphitization of 5B-LIG is also verified bythermogravimetric analysis (TGA) measurement under argon (FIG. 30C). ThePI/H₃BO₃ substrate begins to decompose at 550° C., whereas 5B-LIGremains stable over 900° C. From BET analysis (FIG. 31), the surfacearea of 5B-LIG is 191 m²/g. FIG. 30D shows the pore size distribution of5B-LIG, which are all <10 nm (26 Å, 41 Å and 73 Å).

To confirm the boron doping in the product, X-ray photoelectronspectroscopy (XPS) was performed on a H₃BO₃-loaded sample before andafter laser induction, as shown in FIG. 32 for survey spectra and FIG.33 for elemental spectra. Prior to laser induction, the C1s peakoriginating from PI/H₃BO₃ could be fitted by three sub-peaks: 284.5,285.6 and 288.4 eV, representing C—C, C—N and C—O—C═O bonding,respectively (FIG. 33A). For the O1s peak, two sub-peaks can be found at533.0 and 531.8 eV, representing C—O and C═O bonding (FIG. 33B). Afterlaser induction, the 5B-LIG only showed a single prominent peak at 284.5eV for C1s and 532.9 eV for O1s, and the atomic percentage of carbonincreased from 72% to 84%, whereas oxygen decreased from 19% to 4.3%,indicating that the imide group containing C═O bonding forms a graphiticstructure. Also, the B1s peak (FIG. 33C) shifted from 192.5 eV in B-PIdown to 191.9 eV in 5B-LIG after laser induction, showing that boron inthe LIG sheet was in the oxidized form (BCO₂). The position of N1schanged little after laser treatment (FIG. 33D), but its atomicpercentage dropped from 7.6% to 2.0%, again indicating that the imidegroup is the main reacting site during laser induction process.

To investigate the electrochemical properties of the B-LIG, it wasdirectly patterned into interdigitated electrodes during laser inductionand then fabricated into in-plane MSCs, as shown in FIG. 34A. Asolid-state electrolyte made from poly(vinyl alcohol) (PVA) and H₂SO₄was used to ensure the flexibility of the device (as discussed inExample 3, Applicants have shown that polymeric electrolytes promote abetter electrochemical performance from LIG than conventional aqueouselectrolytes).

To demonstrate the importance of the dehydration reaction of PAA to PI,PAA sheets with or without H₃BO₃ were directly laser induced andfabricated into MSC to first compare their electrochemical performance.Cyclic voltammetry (CV) and charge-discharge (CC) measurements ofcorresponding MSC devices are exhibited and compared in FIGS. 34B-C.Both PAA-derived LIG-MSC and boron-doped PAA-derived LIG-MSC showedsmaller and tilted CV curves compared to boron-free PI-derived LIG-MSCin FIG. 34B, representing a lower capacitance and a higher resistance.The large voltage drop observed at the initial stage of discharge run inPAA-derived LIG-MSC from FIG. 34C also indicates a higher internalresistance. This result shows that the dehydration step from PAA to PIis preferred for successful formation of B-LIG with higher quality andbetter electrical conductivity.

Next, Applicants compared the electrochemical performance of B-LIG withdifferent initial H₃BO₃ loadings. At a scan rate of 0.1 V/s, all CVcurves from xB-LIG-MSCs (x=0, 1, 2, 5, and 8) are pseudo-rectangular, asshown in FIG. 34D, representing good electrochemical double layer (EDL)character. Among them, 5B-LIG-MSC shows the largest areal capacitance(C_(A)), as evidenced by its highest CV current. From FIG. 34E, allgalvanostatic CC curves from B-LIG-MSCs at a current density of 1 mA/cm²show a nearly triangular shape, further confirming the good capacitivebehavior of the devices. Again, 5B-LIG-MSC exhibits the longestdischarge runtime, indicating the best capacitance performance. FIG. 34Fshows the influence of boron content on C_(A), which increases from 0 to5% reaching a maximum ˜4 times greater than undoped-LIG, and thendecreasing slightly at higher loadings. When the boron doping level islow, increasing boron dopants into LIG will increase the hole chargedensity thus enhancing the electrons charge storage. However, after asaturation threshold, additional boron doping might induce morescattering sites for electrons in the LIG sheet, lowering theconductivity of the material, causing the decrease of C_(A). Inaddition, higher H₃BO₃ loadings could inhibit the dehydration process ofPAA, resulting in the retardation of efficient PI formation. As aresult, an optimum content of H₃BO₃ is needed to maximize the deviceperformance.

Because 5B-LIG-MSC shows the highest C_(A) among different H₃BO₃ loadingsamples, it was chosen to further examine the electrochemicalperformance of the 5B-LIG-MSC. FIG. 35A show CV curves of a 5B-LIG-MSCat scan rates of 0.01, 0.02, 0.05 and 0.10 V/s. The maintainedpseudo-rectangular shape of CV curves over different scan ratesrepresents good EDL formation of the devices.

FIG. 35B shows the galvanostatic CC curves at different currentdensities (0.1, 0.2 and 0.5 mA/cm²), all of which are nearly triangular,further confirming their optimal capacitive behaviors. Additional CVcurves at higher scan rates and CC curves at higher current densitiesare shown in FIG. 36 to demonstrate that 5B-LIG-MSC can operate over awide range of scan rates and current densities. The C_(A) determinedfrom these CC curves shows little decrease over current densitiescovering two orders of magnitude, with a maximum of 16.5 mF/cm² at acurrent density of 0.05 mA/cm², which is four times larger than that ofthe non-doped LIG made from the same process without H₃BO₃ incorporated.Furthermore, C_(A) of 5B-LIG-MSC remains over 3 mF/cm² even whenoperated at a high current density of 40 mA/cm², indicating optimalpower performance.

Electrochemical impedance measurements shown in FIG. 37 furtherdemonstrate that both external and internal resistances of 5B-LIG-MSCare lower than that of LIG-MSC. These results indicate faster ionictransport and better electrode-electrolyte interface when the LIGmaterial is doped with boron. The cyclability of 5B-LIG-MSCs was alsotested over 12000 CC cycles at a current density of 1.0 mA/cm² with over90% of the capacitance retained (FIG. 35D), proving high stability ofperformance from the B-LIG-MSC.

In addition to high C_(A), the assembled MSC from 5B-LIG also showsoptimal durability under mechanical stress. When the device was bent andfixed (FIG. 35E) at different bending radii (from 7 to 17 mm), thecalculated C_(A) from discharge runtime remained essentially constant,as shown in FIG. 35F. Furthermore, after 8000 bending cycles at a radiusof 10 mm, the C_(A) of the device was unchanged (FIG. 35G), and CVcurves during different bending cycles as shown in FIG. 35H areidentical to each other, suggesting that bending had little effect onthe electrochemical performance of 5B-LIG-MSC.

To further demonstrate the high capability of 5B-LIG-MSC over non-dopeddevices, a Ragone plot of volumetric power density (P_(V)) vs. energydensity (E_(V)) was compared and shown in FIG. 35I. Under differentP_(V), the E_(V) of 5B-LIG-MSC was 5 to 10 times larger than that ofLIG-MSC without boron doping. To better evaluate its commercialpotential, a Ragone plot of 5B-LIG-MSC with specific areal energydensity and power density is also provided in FIG. 38. The remarkableelectrochemical performance, cyclability over charge-discharge times,and stability under bending makes B-LIG a promising candidate as anenergy storage unit for next-generation flexible and portableelectronics.

In summary, Applicant report in this Example a facile and robust laserinduction process to prepare boron-doped graphene structures frompolyimide films, which can be used as an active material for flexiblein-plane microsupercapacitors. With boron doping, the electrochemicalperformance of B-LIG is enhanced with three times larger arealcapacitance and 5 to 10 times larger volumetric energy density atvarious power densities. Also, the transformation of PAA to PI ispreferred for the successful formation of LIG with high quality and goodelectrochemical property. Meanwhile, the cyclability and flexibility ofthe as-prepared device is well-maintained. Considering the simplicity ofmaterial synthesis in ambient air and the easy device fabrication,boron-doped LIG materials hold promise for energy-storage devices inportable microelectronics.

Example 2.1. Materials Synthesis and Device Fabrication

7.8 g of poly(pyromellitic dianhydride-co-4,4′-oxydianiline amic acid)(PAA) solution (12.8 wt %, 575798-250ML, Sigma-Aldrich) was used asprecursor solution for formation of a polyimide sheet. Various amountsof H₃BO₃ (B0394, Aldrich) (10 mg for 1 wt %, 20 mg for 2 wt %, 50 mg for5 wt %, and 80 mg for 8 wt %) were added to the PAA solution with bathsonication for 30 minutes, and then poured into an aluminum dish andplaced in a vacuum oven at 60° C. and a pressure of ˜120 mm Hg for 3days to evaporate the solvent. The filming process was done in ahydraulic press (Carver, No. 3912) with an applied load of 3×10⁵ Pa at200° C. for 30 minutes to dehydrate the PAA/H₃BO₃ and form the PI/H₃BO₃sheet. Laser induction was then conducted on the PI/H₃BO₃ substrate witha 10.6 μm carbon dioxide (CO₂) laser cutter system (Universal X-660laser cutter platform at a pulse duration of ˜14 μs). The laser powerwas fixed at 4.8 W during laser induction. All experiments wereperformed under ambient conditions. To fabricate in-plane MSCs, LIG waspatterned into 12 interdigitated electrodes with a length of 5 mm, awidth of 1 mm, and a spacing of ˜300 μm between two neighboringmicroelectrodes (FIG. 27B). After that, Pellco® colloidal silver paint(No. 16034, Ted Pella) was first applied on the common areas of bothelectrodes for better electrical contact. The electrodes were thenextended with conductive copper tape which were connected to anelectrochemical workstation (CHI608D, CHI Instruments) for testing.

A Kapton polyimide tape was employed to protect the common areas of theelectrodes from electrolyte. Polymer electrolyte was made by stirring 10mL of DI water, 1 mL of sulfuric acid (98%, Sigma-Aldrich), and 1 g ofpolyvinyl alcohol (M_(w)=50000, Aldrich No. 34158-4) at 80° C.overnight. For the MSC device, ˜0.25 mL of electrolyte was dropped ontothe active B-LIG area on PI substrate, followed by placing the deviceovernight in a desiccator that was connected to a house vacuum (˜120 mmHg) to remove excess water.

Example 2.2. Material Characterization

SEM images were obtained on a FEI Quanta 400 high resolution fieldemission SEM. TEM and HRTEM images were obtained using a JEOL 2100Ffield emission gun transmission electron microscope. TEM samples wereprepared by peeling off 5B-LIG from a PI substrate, followed bysonicating them in chloroform, and dropping them onto a lacey carboncopper grid. Raman spectra were recorded on a Renishaw Raman microscopeusing a 514-nm laser with a power of 5 mW. XRD was conducted on a RigakuD/Max Ultima II with Cu Ku radiation (λ=1.54 Å). The surface area of5B-LIG was measured with a Quantachrome Autosorb-3b BET surfaceanalyzer. TGA (Q50, TA instrument) was carried out from room temperatureto 900° C. at 5° C./min under argon flow. XPS was performed using a PHIQuantera SXM Scanning X-ray Microprobe with a base pressure of 5×10⁻⁹Torr. Survey spectra were recorded in 0.5 eV step size with a passenergy of 140 eV. Elemental spectra were recorded in 0.1 eV step sizeswith a pass energy of 26 eV. All the spectra were corrected using C1speaks (284.5 eV) as references. CV and galvanostatic CC measurementswere performed using a CHI 608D workstation (USA). All of measurementswere conducted under ambient conditions.

Example 2.3. Calculation of Parameters as Indications forElectrochemical Performance of LIG Derived Devices

The specific areal capacitances (C_(A), in mF/cm²) and volumetriccapacitances (C_(V), in F/m³) from galvanostatic charge-discharge (CC)curves can be calculated by the following equations:

$\begin{matrix}{C_{A} = \frac{I}{S \times \left( {{dV}/{dt}} \right)}} & (1) \\{C_{V} = \frac{C_{A}}{d}} & (\; 2)\end{matrix}$

In the above equations, I is the discharge current (in amperes); dV/dtis the slope of galvanostatic discharge curves; and S is total area ofactive positive and negative electrodes. Considering the dimensions of12 such electrodes (5 mm in length and 1 mm in width), S is calculatedas 0.6 cm². d is the thickness of active materials with 25 μm, asrevealed in FIG. 26C inset.

The specific areal (E_(A), in μWh/cm²) and volumetric energy densities(E_(V), in Wh/m³) are calculated using the following equations:

$\begin{matrix}{E_{A} = {\frac{1}{2} \times C_{A} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & (3) \\{E_{V} = {\frac{1}{2} \times C_{V} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & (4)\end{matrix}$

The specific areal (P_(A), in mW/cm²) and volumetric (P_(V), in W/cm³)power densities are obtained from the following equations:

$\begin{matrix}{P_{A} = {\frac{E_{A}}{\Delta\; t} \times 3600}} & (5) \\{P_{V} = {\frac{E_{V}}{\Delta\; t} \times 3600}} & (6)\end{matrix}$

In the above equation, Δt is discharge time (in seconds).

Example 3. Flexible and Stackable Laser Induced Graphene Supercapacitors

In this Example, Applicants demonstrate that laser induction can beutilized to transform commercial polyimide films into porous graphenefor the fabrication of flexible, solid-state supercapacitors. Twodifferent solid-state electrolyte supercapacitors are described, namelyvertically stacked graphene supercapacitors and in-plane graphenemicrosupercapacitors, each with enhanced electrochemical performance,cyclability, and flexibility. Devices with a solid-state polymericelectrolyte exhibit areal capacitance of >9 mF/cm² at a current densityof 0.02 mA/cm², over twice that of conventional aqueous electrolytes.Moreover, laser induction on both sides of polyimide sheets enables thefabrication of vertically stacked supercapacitors to multiply itselectrochemical performance while preserving device flexibility.

In particular, Applicants demonstrate in this Example the fabrication offlexible laser induced graphene (LIG) based super capacitors (SCs) byusing a solid-state polymeric electrolyte, poly(vinyl alcohol) (PVA) inH₂SO₄. Two flexible, solid-state SCs are described: LIG-SCs andLIG-MSCs. These devices show areal capacitance of >9 mF/cm² at adischarge current density of 0.02 mA/cm², which is over twice thatachieved when using aqueous electrolytes. Furthermore, by laserinduction of both sides of the PI sheets, solid state LIG-SCs can bestacked to form high density energy storage devices that multiply theirelectrochemical performance while maintaining flexibility.

FIG. 39A schematically illustrates the process in fabricating flexible,solid-state LIG-SCs. The process begins by first transforming thesurface of a PI sheet into porous graphene under laser induction using acommercially available, computer controlled CO₂ laser cutting system,and then assembling either a single LIG-SC or stacked LIG-SC.

FIGS. 40 and 39B show the photograph of a half-side LIG electrode and atypical single LIG-SC device manually bent to demonstrate its intrinsicflexibility. An advantage of this fabrication method is that LIG can beeasily produced under ambient conditions on both sides of the PI sheetwith a remaining central insulating PI layer to separate them (FIG.39C), which then facilitates layer-by-layer stacking of LIG-SCs.Alternatively, this same technique can also be used to pattern LIG intointerdigitated electrodes for fabrication of solid state in-planeLIG-MSCs (FIG. 41). This one-step approach is both straightforward andcost-effective, and could easily fit into a scalable, roll-to-rollprocess for industrial production of graphene-based energy storagesystems.

The formed LIG showed very similar morphology and graphene properties asthe LIGs in Examples 1-2. FIG. 39C shows a cross sectional scanningelectron microscope (SEM) image, where a thick LIG layer (˜25 μm) isclearly formed on both sides of the PI substrate after laser inductionand is separated by an unexposed middle PI layer that serves toelectrically isolate the top and bottom LIG layers from each other. TheSEM image in FIG. 39D shows the porous structure of LIG and thetransmission electron microscope (TEM) image in FIG. 39E shows thenanoscale ripples and wrinkles in the LIG films. Also, thehigh-resolution TEM (HRTEM) image in the inset of FIG. 39E reveals thatthese LIG sheets contain numerous graphene edges resulting in moreaccessible surface area and therefore better electrochemicalperformance.

The Raman spectrum of LIG in FIG. 43A clearly shows three characteristicpeaks of graphene derived material, specifically, a D peak at ˜1350 cm⁻¹induced by defects, folding or symmetry-broken carbon, G peak at ˜1590cm⁻¹ generated by graphitic carbon, and a 2D peak at ˜2700 cm⁻¹originating from second-order zone boundary phonons. Without being boundby theory, it is envisioned that the D peak could arise from numerousgraphene edges existing in LIG flakes, which are also observed in theabove TEM images.

The XRD pattern in FIG. 43B shows a prominent peak at 2θ=25.60,indicative of an interlayer spacing of ˜3.4 Å between (002) graphiticcrystal planes in LIG. The high degree of graphitization of LIG isfurther supported by thermogravimetric analysis (TGA) under argon (FIG.44), since PI decomposes at ˜550° C., whereas LIG remains stableat >900° C. BET analysis in FIG. 45A shows that the surface area of LIGis ˜330 m²/g with a pore size distribution between 2-10 nm (FIG. 45B).

To investigate its electrochemical performance, LIG was first fabricatedinto a flexible, single LIG-SC by sandwiching a solid, polymericelectrolyte (PVA and H₂SO₄) between two single-sided LIG-PI sheets whichfunctioned both as the working electrode and current collector. Thecyclic voltammetry (CV) curves shown in FIG. 42A were pseudo-rectangularover varying scan rates (5, 10, 20, and 50 mV/s), which is indicative ofgood EDL stability. In addition, FIG. 42B shows that when differentcurrent densities (0.02, 0.05, 0.10, and 0.20 mA/cm²) were applied, thegalvanostatic charge-discharge (CC) curves were nearly triangular,indicating good capacitive behavior. From the initial stage ofdischarge, the negligible voltage drop shows that the device has lowinternal resistance.

Additional CV curves at higher scan rates and CC curves at highercurrent densities can be found in FIG. 46 to show that LIG-SC can becharged and discharged over a wide range of scan rates (5 to 1000 mV/s)and current densities (0.02 to 2.0 mA/cm²). The calculated arealcapacitances (C_(A)) from the CC curves with its corresponding currentdensities are shown in FIG. 42C, with the highest capacitance being 9.11mF/cm² at a corresponding current density of 0.01 mA/cm², comparable tothe values reported in the literature for graphene basedmicrosupercapacitors (0.4 to 2 mF/cm²). Also, the single LIG-SC showsexcellent cycle stability, where after 8000 CC cycles, the deviceretained over 98% of its capacity (FIG. 42D).

Next, the assembled single LIG-SCs performance stability was testedunder mechanical bending. FIG. 47A compares the CV curves of a flexiblesingle LIG-SC over different bending radii (12 mm to 24 mm) andremarkably shows that the bent device exhibits nearly identical behaviorto the flat LIG-SC. Also, FIG. 47B shows that the calculated C_(A) underdifferent bending radii remained almost constant. From FIG. 47C, theC_(A) was well-maintained after 7000 bending cycles at a radius of 14mm, indicating that repeated bending has little effect on itselectrochemical performance. These findings further reinforce theassertion that LIG-SC is a promising candidate for energy storagedevices in flexible, portable, and wearable electronics.

An additional advantage of the aforementioned method is the capabilityof forming LIG on both sides of an individual PI sheet, thus enablingthe fabrication of stacked LIG-SC (FIG. 39). FIGS. 48A-B areillustrations of a series and parallel LIG-SC assembled from stackedsolid-state LIG-SCs, where double-sided LIG sheets are layered withalternating deposits of polymeric electrolyte and capped withsingle-sided LIG-PI sheets. FIGS. 48C-D show the CC curves of a 3-stacksolid-state series and parallel LIG-SC, respectively. Compared to asingle LIG-SC, the stacked series LIG-SC has a 2× higher working voltagewindow, while the stacked parallel LIG-SC shows a 2× longer dischargetime when operated at the same current density, resulting in a 2× highercapacitance. In both configurations, the CC curves present nearlytriangular shapes with miniscule voltage drop indicating negligibleinternal and contact resistances.

Additional CV and CC curves at various scan rates and current densitiesfor the stacked series and parallel LIG-SCs are shown in FIGS. 49-50 todemonstrate their remarkable durability over a wide range of scan ratesand current densities. Even though the SCs are stacked, the assembledstacked LIG-SCs still show high flexibility. FIGS. 48E-F show that thecapacitance of the stacked LIG-SC circuits are nearly 100% of theirinitial value, even after being subjected to several thousand bendingcycles at a bending radius of 17 mm. Additionally, the CV curves atdifferent bending cycles are nearly overlapped (insets of FIGS. 48E-F),indicating well maintained flexibility.

The laser induction process can also be used to synthesize and patternLIG into interdigitated electrodes for the fabrication of in-planeLIG-MSCs (FIG. 41). FIG. 51A is an illustration of a flexible LIG-MSCfabricated on a PI sheet that uses PVA/H₂SO₄ as solid-state electrolyte.FIG. 51B shows CV curves of the LIG-MSC device at different scan rates(0.01, 0.02, 0.05 and 0.1 V/s) with stable pseudo-rectangular shape dueto good EDL formation. FIG. 51C shows the galvanostatic CC curves ofLIG-MSCs at different current densities (0.1, 0.2, 0.5 and 1.0 mA/cm²),all of which are nearly triangular due to their optimal capacitivebehaviors. FIG. 52 shows additional CV curves at higher scan rates andCC curves at higher current densities. The calculated C_(A) from CCcurves at different current densities are plotted in FIG. 51D, where thedevices strikingly exhibit a capacitance of greater than 9 mF/cm² at acurrent density of 0.02 mA/cm². Interestingly, at the same currentdensities the capacitances of the solid-state LIG-MSCs are twice that ofaqueous H₂SO₄ electrolyte LIG-MSCs. Without being bound by theory, it isenvisioned that this improvement could come from the high hydrophobicityof the LIG material and better interface formation between LIGelectrodes and the organic polymer electrolyte.

Furthermore, capacitance of the solid-state LIG-MSCs remains over 1.9mF/cm², even when operated at a higher current density of 30 mA/cm²,indicating high power performance of the device. Electrochemicalimpedance measurements (FIG. 53) further support faster ionic transportand better electrode-electrolyte interface in LIG-MSCs using PVA/H₂SO₄as the electrolyte. The near absence of the semicircle in the case ofMSCs with PVA/H⁺ implies that there is high ionic conductivity at theinterface of the LIG electrode and polymer electrolyte. Also, the higherslope in the Nyquist plot for MSCs with PVA/H⁺ indicates that they havemore capacitive behavior. The cyclability of solid-state LIG-MSCs wasalso tested over 8000 CC cycles with <10% capacitance degradation (FIG.54). In order to test their circuit performance, two single LIG-MSCdevices were connected in either series or parallel configurations asshown in FIG. 55. As expected, the working voltage was doubled whenLIG-MSCs were in series, while the discharge runtime increased nearly100% when LIG-MSCs were in parallel. In both cases, due to thesolid-state electrolyte, the CC curves maintained their triangular shapeand the LIG-MSC showed outstanding flexibility (FIG. 51A inset).

FIG. 51E shows that the in-plane LIG-MSCs made from LIG exhibits nearly100% of its calculated capacitance regardless of bending radii. Similarto the single LIG-SC, CV curves of LIG-MSC over different bending radiiare almost identical to the ones in the flat devices (FIG. 56). After7000 bending cycles, the capacitance remained at its initial value (FIG.51F), further supporting the universality of this laser induction methodin producing energy storage units.

Finally, FIG. 57 is a Ragone plot comparing single LIG-SCs and LIG-MSCsin either aqueous or solid-state polymeric electrolytes to commerciallyavailable electrolytic capacitors and Li thin film batteries. Althoughaluminum (Al) electrolytic capacitors deliver ultrahigh power, theirenergy density is two orders of magnitude lower than LIG-deriveddevices. Similarly, although lithium ion thin-film batteries can providehigh energy density, their power performance is three orders ofmagnitude lower than either single LIG-SCs or LIG-MSCs. Interestingly,when compared to LIG-MSC using 1 M aqueous H₂SO₄ as the electrolyte,LIG-MSC with a solid-state polymer electrolyte stores ˜2× more energy.Also, a comparison between single LIG-SCs and LIG-MSCs shows thatLIG-MSCs have a higher power density than LIG-SC, likely due to thereduced ion diffusion length between the microelectrodes in the LIG-MSCdevice. Ragone plots of single LIG-SCs and LIG-MSCs with specific arealenergy density and power density are also provided in FIG. 58 to betterevaluate their commercial application potential.

In summary, Applicants have demonstrated that by using a laser inductionprocess, commercially available polyimide substrates can be readilytransformed into LIG and then fabricated into flexible and stackable SCswith enhanced capacitive performance. Two different devices, LIG-SCs andLIG-MSCs, were fabricated using PVA/H₂SO₄ as a solid polymericelectrolyte and showed outstanding electrochemical performance,cyclability, and flexibility. The facile fabrication process lendsitself well to commercial scalability.

Example 3.1. Materials Production and LIG Supercapacitor Fabrication

Kapton polyimide (PI, Cat. No. 2271K3, thickness: 0.005″) was purchasedfrom McMaster-Carr and used as received unless noted otherwise. Laserinduction of graphene was conducted with a 10.6 μm CO₂ laser system(Universal X-660 laser cutter platform) at a pulse duration of ˜14 μs.All experiments were conducted under ambient conditions using 4.8 W oflaser power. Two types of LIG based SCs were fabricated: single orstacked LIG-SCs and in-plane LIG-MSCs. For single or stacked LIG-SCs,LIG was produced either on one side or both sides of the PI sheet withan active area of 2 cm×3 cm, whereas for MSCs, LIG was patterned intointerdigitated electrodes with a length of 5 mm, a width of 1 mm, and aspacing of ˜300 μm between two neighboring microelectrodes.

In both types of structures, Pellco® colloidal silver paint (No. 16034,Ted Pella) was applied on the common areas of each electrode for betterelectrical contacts. The electrodes were then extended with conductivecopper tape and connected to an electrochemical workstation. A Kapton PItape was employed to protect the common areas of the electrodes fromelectrolyte (FIGS. 41-42). Polymer electrolyte was made by mixing andstirring 10 mL of DI water, 1 mL of sulfuric acid (98%, Sigma-Aldrich),and 1 g of polyvinyl alcohol (M_(w)=50000, Aldrich No. 34158-4) at 80°C. overnight.

Solid-state LIG-SCs were fabricated by dropping ˜1 mL of PVA-H₂SO₄ ontoa LIG-PI substrate and then sandwiching it with a second LIG-PIsubstrate. Finally, the device was placed in a desiccator that wasconnected to house vacuum (˜10 mmHg) to remove excess water overnight.For LIG-MSC devices, ˜0.25 mL of PVA-H₂SO₄ was dropped onto the activeLIG area on the PI substrate, followed by placing the device overnightin a desiccator that was connected to house vacuum to remove excesswater. For comparison, the MSCs with aqueous electrolyte were alsofabricated by dropping ˜0.2 mL 1 M H₂SO₄ onto the active LIG on PIsheets.

Example 3.2. Characterization

SEM images were taken on a FEI Quanta 400 high resolution field emissionSEM. The TEM and HRTEM images were taken using a JEOL 2100F fieldemission gun transmission electron microscope. TEM samples were preparedby peeling off LIG from the PI substrate, followed by sonicating them inchloroform, and dropping them onto a lacey carbon copper grid. Ramanspectra were recorded on a Renishaw Raman microscope using 514-nm laserwith a power of 5 mW. XRD was conducted on a Rigaku D/Max Ultima II withCu Kα radiation (λ=1.54 Å). The surface area of LIG was measured with aQuantachrome Autosorb-3b BET surface analyzer. TGA (Q50, TA instrument)was carried out at room temperature to 900° C. at 5° C./min under argon.CV and constant current CC measurements were conducted under ambientconditions using a CHI 608D workstation (USA).

Example 3.3. Calculation of Parameters as Indications for theElectrochemical Performance of LIG Based Devices

The specific areal capacitances (C_(A), in mF/cm²) and volumetriccapacitances (C_(V), in F/m³) from galvanostatic charge-discharge (CC)curves can be calculated using Equations 1 and 2:

$\begin{matrix}{C_{A} = \frac{I}{S \times \left( {{dV}/{dt}} \right)}} & (1) \\{C_{V} = \frac{C_{A}}{d}} & (\; 2)\end{matrix}$

In the above equations, I is the discharge current (in amperes), dV/dtis the slope of the galvanostatic discharge curve immediately followingthe voltage drop, S is the total area of the active positive andnegative electrodes. In LIG-SC, S is the active area of LIG (2 cm×3 cm=6cm²). As for LIG-MSC, S is the total area of LIG microelectrodes (0.05cm²×12=0.6 cm²). d is the thickness of active materials with 25 μm asindicated in the FIG. 39C inset. The specific areal (E_(A), in μWh/cm²)and volumetric energy densities (E_(V), in Wh/m³) are calculated inEquations 3 and 4:

$\begin{matrix}{E_{A} = {\frac{1}{2} \times C_{A} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & (3) \\{E_{V} = {\frac{1}{2} \times C_{V} \times \frac{\left( {\Delta V} \right)^{2}}{3600}}} & (4)\end{matrix}$

The specific areal (P_(A), in mW/cm²) and volumetric (P_(V), in W/cm³)power densities are obtained from Equations 5 and 6:

$\begin{matrix}{P_{A} = {\frac{E_{A}}{\Delta\; t} \times 3600}} & (5) \\{P_{V} = {\frac{E_{V}}{\Delta\; t} \times 3600}} & (6)\end{matrix}$

In the aforementioned equations, Δt is discharge time (in s).

Example 4. Effect of Controlling Wavelength for Production of LaserInduced Graphene

Rapid heating of polyimides by absorption of a focused CO₂ laser beam isan exemplary process by which a polymer is converted into a graphenematerial. In some embodiments, the CO₂ laser overlaps with a vibrationalabsorption band of the polyimide, which is preferred for the conversionof the laser beam into heat. The energy density depends on both the spotsize and the penetration depth of the beam into the material. Assumingequal spot sizes, when the beam is strongly absorbed, the energy isdeposited in a thinner layer, leading to more rapid heating. On theother hand, weak absorption will lead to a larger volume absorbing thelight, slower heating and less efficient conversion to graphene. Insituations where greater penetration of the graphene formation isdesired, the laser intensity may be increased either by focusing moretightly or increasing the laser power to produce the necessary energydensity. The penetration depth, or absorption depth, is controlled bythe wavelength of the laser. Hence, a wavelength-tunable laser isimportant for controlling the depth of the graphene formation, andthereby introduces the capability for making 3-dimensional structures inthe LIG films. Furthermore, one can use a two-photon process, whereinmultiple photons (e.g., two photons) cross to induce localized heatingin a 3D block, for 3D printing methods.

FIG. 59 provides an absorption spectrum of a polyimide film. Thespectrum shows a strong absorption band in the 9 to 11 micrometer range.The four solid lines represent center wavelength of the of tworotational-vibrational branches for two vibrational bands of the tunableCO₂ laser. The center frequency of each band is 9.3, 9.5, 10.3 and 10.6micrometers. Each of these four bands consists of a number of rotationallines, which are individually selectable. This is represented by thedotted lines on either side of the solid line on the spectrum in FIG.59. The 9.3 micrometer band has a tuning range of ≈0.15 micrometers, andthe other three bands have tuning ranges of ≈0.2 micrometers.

The availability to choose from many wavelengths allows selection of awide range of penetration depths into a polymer film by changing thewavelength of the laser (e.g., CO₂ laser). This also provides amechanism to make vertical 3D structures into a polymer film. A stronglyabsorbed wavelength is focused on the surface to create a narrow andshallow line of LIG. Then the focus is shifted to below the surface, andthe laser wavelength is changed to allow greater penetration. Next, thepartially attenuated converging beam now coming to a focus below the LIGline already made. The porous LIG material allows the gases to escape asmore LIG is generated below the surface layer. The process can berepeated with an even deeper focus and the laser tuned furtheroff-resonance for greater penetration. This way, vertical structuressuch as deeper lines are created. One way to optimize the generation ofsuch 3D structures is that the incoming beam is divided into two parts,which straddle the first shallow line and pass on either side as theyconverge to the subsurface focal point. The focal point may be shiftedoff the axis of the initial graphene line on the surface to providesubsurface “tunneling”, as long as there is a channel of porous graphenefor the gases to escape.

An alternative way to construct 3D structures is to add a new layer ofpolymer film or liquid precursor by spraying or flooding the surface.Then the focal point is moved up to generate a new LIG line on top ofthe existing LIG material below. Since the added liquid or sprayed-onmaterial may have a different absorption strength than the LIG materialalready formed, then the wavelength is optimized to form LIG in thenewly deposited material.

FIG. 60 is a drawing showing the use of visible lasers and an option ofcoupling into a controlled atmosphere chamber with an optical fiber.This permits the careful control of the environment in the chamber fortermination of the graphene edges with specific gases, and for the useof multiple laser sources. The optical fiber coupling could also be usedwith an NSOM (not illustrated). Without further elaboration, it isbelieved that one skilled in the art can, using the description herein,utilize the present disclosure to its fullest extent. The embodimentsdescribed herein are to be construed as illustrative and not asconstraining the remainder of the disclosure in any way whatsoever.While the embodiments have been shown and described, many variations andmodifications thereof can be made by one skilled in the art withoutdeparting from the spirit and teachings of the invention. Accordingly,the scope of protection is not limited by the description set out above,but is only limited by the claims, including all equivalents of thesubject matter of the claims. The disclosures of all patents, patentapplications and publications cited herein are hereby incorporatedherein by reference, to the extent that they provide procedural or otherdetails consistent with and supplementary to those set forth herein.

What is claimed is:
 1. A method of producing a graphene material,wherein the method comprises: exposing a polymer to a laser source,wherein the polymer is in the form of a substrate, and wherein thepolymer lacks graphene oxide and graphite oxide; and wherein theexposing results in formation of graphene, and wherein the graphene isderived from the polymer.
 2. The method of claim 1, wherein the exposingcomprises tuning one or more parameters of the laser source.
 3. Themethod of claim 2, wherein the one or more parameters of the lasersource are selected from the group consisting of laser wavelength, laserpower, laser energy density, laser pulse width, gas environment, gaspressure, gas flow rate, and combinations thereof.
 4. The method ofclaim 2, wherein a wavelength of the laser source is tuned to match anabsorbance band of the polymer.
 5. The method of claim 1, wherein thepolymer is chosen such that an absorbance band of the polymer matchesthe excitation wavelength of the laser source.
 6. The method of claim 1,wherein the laser source is selected from the group consisting of asolid state laser source, a gas phase laser source, an infrared lasersource, a CO₂ laser source, a UV laser source, a visible laser source, afiber laser source, near-field scanning optical microscopy laser source,and combinations thereof.
 7. The method of claim 1, wherein the lasersource is a CO₂ laser source.
 8. The method of claim 1, wherein thelaser source has a wavelength ranging from about 20 nm to about 100 μm.9. The method of claim 1, wherein the laser source has a power rangingfrom about 1 W to about 100 W.
 10. The method of claim 1, wherein thepolymer is in the form of at least one of sheets, films pellets,powders, coupons, blocks, monolithic blocks, composites, fabricatedparts, electronic circuit substrates, and combinations thereof.
 11. Themethod of claim 1, wherein the polymer is selected from the groupconsisting of homopolymers, vinyl polymers, block co-polymers,carbonized polymers, aromatic polymers, cyclic polymers, polyimide (PI),polyetherimide (PEI), polyether ether ketone (PEEK), and combinationsthereof.
 12. The method of claim 1, wherein the polymer comprises adoped polymer.
 13. The method of claim 12, wherein the doped polymercomprises a dopant selected from the group consisting of heteroatoms,metals, metal oxides, metal chalcogenides, metal nanoparticles, metalsalts, organic additives, inorganic additives, metal organic compounds,and combinations thereof.
 14. The method of claim 1, wherein the polymercomprises a boron doped polymer.
 15. The method of claim 1, wherein theexposing comprises exposing a surface of a polymer to a laser source,wherein the exposing results in formation of the graphene on the surfaceof the polymer.
 16. The method of claim 15, wherein the exposingcomprises patterning the surface of the polymer with the graphene. 17.The method of claim 15, wherein the graphene becomes embedded with thepolymer.
 18. The method of claim 15, wherein the polymer comprises afirst surface and a second surface, wherein the first surface is exposedto the laser source, and wherein the graphene forms on the first surfaceof the polymer.
 19. The method of claim 18, wherein the first surfaceand the second surface are exposed to the laser source, and wherein thegraphene forms on the first surface and the second surface of thepolymer.
 20. The method of claim 18, wherein the first surface and thesecond surface are on opposite sides of the polymer.
 21. The method ofclaim 1, wherein the exposing results in conversion of the entirepolymer to graphene.
 22. The method of claim 1, wherein the formedgraphene material consists essentially of the graphene derived from thepolymer.
 23. The method of claim 1, wherein the graphene is selectedfrom the group consisting of single-layered graphene, multi-layeredgraphene, double-layered graphene, triple-layered graphene, dopedgraphene, porous graphene, unfunctionalized graphene, pristine graphene,functionalized graphene, oxidized graphene, turbostratic graphene,graphene coated with metal nanoparticles, metal particles coated withgraphene, graphene metal carbides, graphene metal oxides, graphene metalchalcogenides, and combinations thereof.
 24. The method of claim 1,wherein the graphene comprises porous graphene.
 25. The method of claim1, wherein the graphene comprises doped graphene.
 26. The method ofclaim 25, wherein the doped graphene comprises a dopant selected fromthe group consisting of heteroatoms, metals, metal oxides, metalnanoparticles, metal chalcogenides, metal salts, organic additives,inorganic additives, and combinations thereof.
 27. The method of claim1, wherein the graphene comprises boron-doped graphene.
 28. The methodof claim 1, wherein the graphene has a surface area ranging from about100 m²/g to about 3,000 m²/g.
 29. The method of claim 1, wherein thegraphene has a thickness ranging from about 0.3 nm to about 1 cm. 30.The method of claim 1, wherein the graphene comprises a polycrystallinelattice.
 31. The method of claim 30, wherein the polycrystalline latticecomprises ring structures selected from the group consisting ofhexagons, heptagons, pentagons, and combinations thereof.
 32. The methodof claim 1, further comprising a step of incorporating the graphenematerial into an electronic device.
 33. The method of claim 32, whereinthe electronic device is an energy storage device or an energygeneration device.
 34. The method of claim 32, wherein the electronicdevice is selected from the group consisting of super capacitors, microsupercapacitors, pseudo capacitors, batteries, micro batteries,lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries,electrodes, conductive electrodes, sensors, photovoltaic devices,electronic circuits, fuel cell devices, thermal management devices,biomedical devices, and combinations thereof.
 35. The method of claim32, wherein the incorporating comprises stacking a plurality of graphenematerials, wherein the stacking results in formation of a verticallystacked electronic device.
 36. The method of claim 32, wherein theincorporating results in formation of at least one of vertically stackedelectronic devices, in-plane electronic devices, symmetric electronicdevices, asymmetric electronic devices, and combinations thereof. 37.The method of claim 32, wherein the graphene is utilized as at least oneof an electrode, current collector or additive in the electronic device.38. The method of claim 32, further comprising a step of associating theelectronic device with an electrolyte.
 39. The method of claim 38,wherein the electrolyte is selected from the group consisting of solidstate electrolytes, liquid electrolytes, aqueous electrolytes, organicsalt electrolytes, ion liquid electrolytes, and combinations thereof.40. The method of claim 38, wherein the electrolyte is a solid stateelectrolyte.
 41. The method of claim 32, wherein the electronic devicehas a capacitance ranging from about 2 mF/cm² to about 1000 mF/cm². 42.The method of claim 32, wherein the capacitance of the electronic deviceretains at least 90% of its original value after more than 10,000cycles.
 43. The method of claim 32, wherein the electronic device haspower densities ranging from about 5 mW/cm² to about 200 mW/cm².
 44. Themethod of claim 1, further comprising a step of separating the formedgraphene from the polymer to form an isolated graphene.
 45. The methodof claim 44, further comprising a step of incorporating the isolatedgraphene into an electronic device.